Protection

Cyber Security and Information Infrastructure Protection - Practical measures for critical infrastructure protection, intrusion prevention and threat assessment.
Deception Toolkit - Make your system seem to have network security bugs, and log attack attempts.
FakeBo - Fakes trojan servers (Back Orifice, NetBus) and logs every attempt from client.
Flawfinder - Examines source code looking for security weaknesses.
Guarded Memory Move (GMM) - The GMM library can be used to prevent and study buffer overflows exploits
Libsafe - Free software (GNU license) from Bell Labs for protecting internet servers from buffer overflow attacks, one of the most commonly exploited security vulnerabilities.
Samhain - A tool for file integrity checking that optionally can be used as a client/server application for centralized monitoring of networked hosts.
TCP Wrappers and other security tools - This is the main FTP site for security tools and papers from Wietse Venema.
Tripwire Security Systems, Inc. - Tripwire, file integrity assessment tool for UNIX.