Wired Equivalent Privacy (WEP) is fast becoming the most insecure
wireless encryption for networks. WPA, on the other hand, is
significantly more difficult to crack. WEP (either 64-bit or 128-bit)
can be cracked easily using Backtrack 3 which is a Linux distro and one
of the most popular tools for the job.
Note, don’t use this for malicious behavior (we have to say that
legally). Anyways, cracking a WEP encryption can be done fairly
easily. While it’s not a one click solution, this step by step security tutorial shows you how to hack WEP using a wireless adapter that’s capable of packet injection, BackTrack 3, and of course a Wi-Fi access point with WEP (not WPA).
The idea is to attack a WEP enabled WiFi access point, capture
packets from the network, and then decrypt the WEP key. There may be
hits and misses along the way as a lot depends on the Wi-Fi signal
strength and the hardware being used.