Some useful tools:
Anti-Spyware -- Block or disable advertiser-sponsored programs that secretly transmit information back to companies.
- Ad-Aware
- Aureate/Radiate Remover
- Flow Protector

Anti-Trojan Horse -- Detect, block, and remove remote access Trojan Horse programs.
- BODetect
- The Cleaner
- Jammer

Anti-Virus -- Detect, remove, and block viruses.
- eSafe Protect Desktop
- F-Prot
- InoculateIT

Bulk Emailers -- Send mail to large lists.
- Express Mail Server
- Stealth Mass Mailer

Cache & Cookie Cleaners -- Protect your privacy by completely removing Cookies and Internet Cache.
- AdSubtract SE
- Complete Cleanup
- Cookie Crusher

Desktop Security -- Generate good passwords and protect your computer while you are away.
- Benjamin Password Generator
- Fake DOS
- ISS Complock II

Disassemblers -- Reveal the assembly language source code of programs so you can see how they work.
- IDA Pro Disassembler
- Letun Disassembler

DNS Lookup -- Verify a domain's existence, and perform Ping, TraceRoute, WhoIs, Finger, and more.
- Cyberkit
- DNS Workshop
- Domain Searcher

Encryption Cracker -- Crack files encrypted with DES.
- BrydDES

File Encryption -- Scramble your data using a variety of algorithms, to keep your information safe.
- Absolute Security
- Blowfish-C
- Blowfish-Java

File Integrity Checkers -- Detect changes in your files that could someone has accessed your computer.
- Veracity

File Shredders -- Securely delete files to prevent access by forensics and recovery programs.
- ASL File Wiper
- Assure
- BCWipe

Forensics -- Retrieve information from deleted files and formatted disks.
- Directory Snoop
- Disable
- Disk Drive Analysis

Hex Editors -- Look at hidden data inside files and disk sectors, and modify contents.
- ASL HexView
- Frhed
- Hex Editor

Honey Pot Traps -- Catch and counter-attack hackers.
- NetBuster
- Tambu UDP Scrambler

How To -- Information about hacking written by hackers.
- The Complete Social Engineering FAQ
- Countermeasures
- The Ethics of Hacking

Intrusion Detection -- Block or monitor the ports on your computer detect probes and intrusion attempts.
- Anti-Hack
- AntiSniff
- Attacker

IRC Clients -- Connect to Internet Relay Chat (IRC) communities where hackers meet.
- MIRC
- Pirch98
- Visual IRC

Keystroke loggers -- See what others are doing with your computer in your absence.
- 2Spy
- AppsTraka
- KeyKey 2000

Packet Sniffers -- Capture and analyze all information traveling across a network.
- Network Sniffer
- TraceWolf Packet Sniffer

Parental Control -- Limit and monitor Internet access and program use on your computer.
- ChatNANNY
- Enuff

Password Recovery -- Recover forgotten passwords.
- 007 Password Recovery
- Access Data
- Advanced Zip Password Recovery

Port Scanners -- Analyze ports on your network to detect vulnerabilities.
- AA Tools
- AntiSniff
- Internet ports

Remote Monitoring -- Silently monitor a computer at another location.
- NetBus Pro
- PC Spy
- Qpeek

Rollback -- Return your computer to a previous state to recover from a virus, system crash, or hacker attack.
- ConfigSafe
- Aladdin FlashBack
- System Safe

Spam Fighters -- Block or filter incoming e-mail.
- Spam Buster
- Spam Hater
- Spam Killer

Steganography -- Hide data in graphics or sound files.
- Contraband
- dc-Steganograph
- Gif-It-Up

System Locks -- Keep unauthorized users from accessing your computer.
- DesktopShield 2000
- Klik-Lok
- Workstation Lock

Voice Encryption -- Use this program to encrypt voice transmissions over the Internet or other networks.
- PGPFone

Vulnerability Scanners -- Scan your computer or network against a database of known exploits and openings.
- Kane Security Analyst
- Retina

Web Site Protection -- Protect your Web site from getting attacked or abused.
- WebAgain
- WebCrypt