BackTrack 4 is a Linux distribution distributed as a Live CD which resulted from the merger of WHAX (previously Whoppix) and the Auditor Security Collection, which is used for penetration testing. It allows the user to include customizable scripts, additional tools and configurable kernels in personalized distributions. The BackTrack project was created by Mati Aharoni and Max Moser and is a collaborative effort involving the community.
BackTrack is intended for all audiences from the most savvy security professionals to early newcomers to the information security field. Although BackTrack contains a lot of tools for testing how hard the security for a system, but it is more commonly being used to crack WEP and WPA wireless passwords as it comes with airmon-ng, airodump-ng, aireplay-ng and aircrack-ng. BackTrack 4 uses newer linux kernal has more updated drivers to support more hardware especially wireless cards. If a system can run BackTrack 4 without problems, all you need to do is learn a few command lines and you’re on your way to cracking WEP and WPA. More conveniently, there are tons of video tutorial on YouTube about hacking wireless with BackTrack.
You can download BackTrack 4 Final from this its official website. Currently BackTrack 4 was released about 2 months ago and has already achieved nearly half a million downloads.