Packetstorm
- Security updates and news bulletins, mostly Linux but also NT. Provides software tips and links.
- http://www.packetstormsecurity.org/

LinuxSecure
- This site on Linux and security covers firewalls (iptables), intrusion detection systems (snort), securing services, and Linux security in general. The aim is to provide information about protection, detection, and reaction with respect to attacks.
- http://www.linuxsecure.de

SSH, the Secure Shell: The Definitive Guide
- This is a companion website for "SSH: The Secure Shell The Definitive Guide" by Daniel Barrett and Richard Silverman (O'Reilly, 2003). It contains technical details on the SSH as well as sample book material.
- http://www.snailbook.com

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.
- http://passwordms.sourceforge.net/

Googgun Technologies Praetor module
- Praetor is a kernel-based "Security Enabler" for Linux that provides fine-grained access control.
- http://www.googgun.com/

StegFS - A Steganographic File System for Linux
- Not only does it encrypt data, it also hides it such that it cannot be proved to be there.
- http://www.mcdonald.org.uk/StegFS/

Linuxbroker - Security
- Linuxbroker provides all types of resources you need like Linux newsgroups search engine, daily news, howtos, applications releases tracking and security alerts.
- http://security.linuxbroker.com

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.
- http://www.intersectalliance.com/projects/Snare/index.html

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.
- http://www.hackinglinuxexposed.com/

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.
- http://www.ecst.csuchico.edu/~dranch/LINUX/index-linux.html

Exploit World - Linux Section
- Known vulnerabilities on the Linux system with detailed description.
- http://www.insecure.org/sploits_linux.html

Linux Security
- Linux Security, server hardening, 1U server, 24x7 server admin, monitoring, IDS, NDS, firewalls
- http://www.linux-sec.net/