This MIT course on network and computer security covers topics such as security in multi-user distributed systems, cryptography, authentication, intrusion detection, and many other security topics.

Directory of firewall and computer security information includes tools, reviews of several popular packages, patches, employment, articles, and more.

The FireWall ToolKit (FWTK) is a set of proxies which you can use to build your own firewall. This site provides downloads, documentation, FAQ and patches.