Network Intrusion

Robert Graham's Infosec publications : includes a lot of interesting information, including a list of port seen from a security point of view.

NDISbench : test your network intrusion detection system.

Security Focus : the best security site around.

The Common Intrusion Detection Framework homepage.

Shadow's Homepage - the US Navy Intrusion detection system.

Snort - a lightweight network intrusion detection system.

Nessus - the freeware, open source vulnerability scanner.

Buffer Overflow Primer by DilDog.

50 tools for the hacker, from the insecure.org site.

ntobjective's free tools - IP packet creator, forensic tools, log cleaner...

cotse - information resources for the IT professional.

Counterpane's research pages.