Linux is a great operating system to learn about network security. If you are interested in learning more about the information security field then Back Track Linux distribution is something you should definitely try. The latest stable release is Back Track 4 which was released on January 9th 2010 and includes the most comprehensive security related tools. Back Track 4 is not only geared towards professionals but for all types of skill levels. You can use Back Track as your primary OS or boot it from live DVD or a thumb drive. It is a very popular penetration testing distro which allows you to learn about network vulnerability and many other related security issues. It includes tons of applications and is based on the Ubuntu distribution. To download Back Track 4 go to their website.