This is a great video tutorial series to understand rootkits by Corey Nachreiner.
Rootkits Part 1Corey defines rootkits, then demonstrates a real rootkit found in the wild. See what investigative processes it hides from, how an attacker configures it, and more.
http://www.watchguard.com/education/video/play.asp?vid=root1-cubecastRootkits Part 2Corey explains inline function hooking, what kinds of Windows functions are susceptible to hooking, and how rootkits use hooking for backdoor access to your network.
http://www.watchguard.com/education/video/play.asp?vid=root2-cubecastRootkits Part 3Topics chosen by user vote. Kernel mode rootkits; leading techniques and tools for detecting rootkits; how your Firebox helps stop rootkits from entering your network.
http://www.watchguard.com/education/video/play.asp?vid=root3-cubecast
Tutorials : Hacking Scenarios 
Hadnagy : [Article]-An Insider`s Look at the Social-Engineer.Org SE CtF at DEFCON
Editor-In-Chief : Free Webcast: Don't Pick the Lock, Steal the Key - PW Auditing with Metasploit
Links to cool sites. : Ninja-Sec Challenge You !
Tools : Nmap 6 Released
