Screaming Penguin - Source Does Matter

Auditing your security setup is essential. Once you are done with that fancy secure box, gateway, firewall, bastion host, whatever, audit it. There are many tools and articles that can be used to perform a security audit (often, these are the same tools potential hackers use.) The linked rootprompt article touches on all of the main items and provides links to the tools. It is a great overview and includes a related section on securing a Linux box (many of the points parallel my Linux basic security howto, both are worth a read.)   Rootprompt: Auditing Your Firewall