" As important as security is, remaining current with every development is hard, and evaluating possible vulnerabilities across a network can be quite a chore. You need a way to both automate tests and make sure you're running the most appropriate and up-to-date tests. Open Vulnerability Assessment System
(OpenVAS) is a network security scanner that includes a central server and a graphical front end. The server allows you to run several different network vulnerability tests (NVT) written in Nessus Attack Scripting Language (NASL), which OpenVAS updates frequently.
OpenVAS is a fork of version 2.2 of the classic Nessus scanner. About three years ago, Nessus dropped the GPL, opting for a more commercial approach for its version 3.0. It decided to give away the software but charge for quick NVT upgrades and apply other restrictions. (Some restrictions were recently lifted for home users.) In July, OpenVAS came out with its 1.0 release and has made minor updates to it since then. All code is under the GPL."
Read more: http://www.linux.com/feature/149492