Backtrack 5 is one of my favorite operating systems. Backtrack has so many tools like metasploit, ophcrack, wireshark, kismet and many more. Backtrack has tools to find computers on the network and what ports are open on them. You can also use this to hack into computers.
BackTrack provides users with easy access to a comprehensive and large collection of security-related tools ranging from port scanners to password crackers. Support for Live CD and Live USB functionality allows users to boot BackTrack directly from portable media without requiring installation, though permanent installation to hard disk is also an option.
Video From Backtrack 5:
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