Securing a Linux System

A tutorial on how to configure a fresh Linux installation for greater security.
* http://www.stuartellis.eu/articles/securing-linux

Brief idea about Pluggable Authentication Modules for Linux. 

* http://www.linuxjournal.com/article/2120

Configuring a secure Ubuntu Linux Virtual Private Server

* http://blog.dhananjaynene.com/2009/10/configuring-a-secure-ubuntu-linux-virtual-private-server/