AutomaticSecurityUpdates - How to set up Ubuntu to install security updates automatically
StrongPasswords - How to generate and use strong passwords in Ubuntu
StricterDefaults - Default settings that you could change if you wanted stricter settings at the cost of convenience
InstallingSecurityTools - A guide to installing several security applications in Ubuntu
IptablesHowTo - An introduction to the powerful Linux IPTables firewall
SinglePacketAuthorization - Advanced "firewall knocking" via cryptographic authentication
Network Intrusion Detection System (IDS) - Setting up Snort and acidbase to serve as an IDS
Data Leak Prevention
MyDLP - Installation and Internet / e-mail configuration instructions to prevent data leak from network with MyDLP.
BastilleLinux - The Bastille Linux Security Hardening Tool
BitDefender - How to install Bit Defender Linux Edition
FileIntegrityAIDE - File integrity monitoring and verification with AIDE
RKhunter - How to use RKhunter.
AdvancedOpenSSH - Advanced OpenSSH configuration for enhanced security
SecureDeletion - How to erase (wipe) data from hard discs in a way that hampers data recovery
Encrypted Filesystems - Index page containing step-by-step instructions on encrypting entire root filesystems and portable devices
FolderEncryption - How to encrypt a folder with encfs, and automatically mount it at login
GPG Key - How to create/manage a GPG key and use it in your favorite E-Mail client
GPGKeyOnUSBDrive - How to store your GPG key securely on an encrypted USB flash drive
OpenSSL - OpenSSL Secure Sockets Layer implementation information
CommonAccessCard - Department of Defence Common Access Card (CAC) for Public key infrastructure (PKI) Authentication
AntiVirus - About antivirus programs in Gnu&Linux. To summarise, they are the best way to scan a Windows partition or to block an infected file that people are passing around to each other.
Linuxvirus - An overview of the types of malware generally found on computers and descriptions of specific malware that works on Linux (usually made to test the security of systems).
ClamAV - How to install ClamAV on your HD
Tor Project - Anonymous web surfing using Tor and Polipo.