Some Linux distributions, like BackTrack or Kali, are security-focused distros for testing security systems. That means you can use them to learn how to, say, hack WEP or WPA Wi-Fi passwords, which is a great way to learn a bit more about your own network security and how to protect yourself from similar attacks. Of course, we don't recommend using these powers for evil—but knowing evil's tricks gives you a good path to preventing them.