Examines source code looking for security weaknesses.

A tool for file integrity checking that optionally can be used as a client/server application for centralized monitoring of networked hosts.

Tripwire, file integrity assessment tool for UNIX.

Practical measures for critical infrastructure protection, intrusion prevention and threat assessment.

The GMM library can be used to prevent and study buffer overflows exploits

Make your system seem to have network security bugs, and log attack attempts.

Fakes trojan servers (Back Orifice, NetBus) and logs every attempt from client.

This is the main FTP site for security tools and papers from Wietse Venema.

Free software (GNU license) from Bell Labs for protecting internet servers from buffer overflow attacks, one of the most commonly exploited security vulnerabilities.