These two sites are an excellent source of tools, papers, security patches, and other Internet security resources.
This archive is maintained by the COAST computer and network security project at Purdue University (see the description under the COAST WWW page above) under the direction of Gene Spafford. It contains a large collection of software and papers related to UNIX and network security, collected from all over the world.
Collected abstracts for the many tools and papers on the server are in the /pub/aux directory:
ftp://coast.cs.purdue.edu/pub/aux/tools.abstract
ftp://coast.cs.purdue.edu/pub/aux/documents.abstract
This site contains all of the Computer Emergency Response Team Coordination Center (CERT-CC) past advisories (see the discussion of CERT-CC under "Organizations" below), as well as a small collection of tools and papers.