A Little Bit of Crypto - I have been trying to figure out to "collision resistant" some of these standard hash functions are. It is a tough concept to get my head around. I figure...
Nessus is available on Windows and Linux based systems. It is purportedly the most popular vuln scanner. It can scan for a number of things such as remove control and access, misconfiguration, bad passwords, and Denial of Service exploits. The tool can help you prepare for a security audit.
You write tests for Nessus to perform. The tests are written in a custom scripting language called NASL. You can subscript to receive tests from Tenable. The program output can be formatted in text, HTML, or even XML formats. A free competitor in the vuln scanning space is OpenVAS.