Bastille Linux - Attempts to "harden" (tighten the configuration of) a Red Hat or Mandrake Linux installation.
The Digital Underground - Computer and Technology articles, and a members page for the "digital underground" community with text, programs, and security information.
Dranch: TrinityOS - Step by step, example driven, HOWTO on building a Linux box with an aim towards strong security. Also, links to resources and mailing lists.
Hacking Linux Exposed - Companion Website to Hacking Linux Exposed, Osborne/McGraw-Hill. Source code from the book, updates, and other tools to secure your Linux system.
Linux Audit and Intrusion Detection - InterSect Alliance are the creators of the SNARE Linux C2-style Audit module, and have a consulting background in advanced audit analysis, intrusion detection systems, and forensics for Unix and other operating systems.
Linux Security - Linux Security, server hardening, 1U server, 24x7 server admin, monitoring, IDS, NDS, firewalls
Linux Security - Information collected from many sources: feature articles, advisories, news, documentation, forums, links.
Linuxbroker - Security - Linuxbroker provides all types of resources you need like Linux newsgroups search engine, daily news, howtos, applications releases tracking and security alerts.
NiftyBox Advisor - Open-source security tools including "Advisor" to automatically notify an admin when a security advisory affects an installed package.
Packetstorm - Security updates and news bulletins, mostly Linux but also NT. A lot of software tips and links.
Password Management System - Designed for System Administrators, to handle user logins for several computers running Linux. It works with a console interface, based on the CDK library that uses ncurses. Import data from csv files and export to text files with a free definable format.
Penetrator Megablaster - A kernel module that detects and stops overflow attacks, like Linux Buffer Overflow attack security, which aim to get an interactive access to the system.
RootFront - UNIX/Linux security news, exploits, security articles, FAQs, documentation, downloads and other resources.
Rubberhose - A filesystem that can be used to hide files on the disk by dissolving them in the innocent disk content.
Sardonix.org - DARPA-funded community project to audit the source of all Linux applications for security vulnerabilities.
Security News - Dedicated to providing information and news to educate administrators and security enthusiasts.