You can brute force the WPA2 passpharse with the help of GPUs. Here is my discoveries on April 16, 2010 and May 22, 2011.
If the wifi router is equipped with WPS (Wifi Protected Setup) and it is enabled, to crack it is very easy with the tool namely reaver.
In additional, it is risky to use public wifi or public free wifi too. No matter they have passpharse or not. (Please refer to "
See Also" for details) You are also be informed that there are some high power and long range wifi adaptors in the market.
Alfa Network produces some high power and long range wifi adaptors, such as Alfa AWUS036H and Alfa AWUS036NHR. They can connect to the vicitm's wifi router in the distance of 1KM+ away.
That's all! See you.
See Also :
HOWTO : Sniffing SSL with ettercap on Back|Track 5
HOWTO : Protect you from being ARP spoofing