A tool named as FERN WIFI CRACKER using which in general you can hack WEP as well as WPA secured WIFI networks and this GUI based application is quite easy to use plus, it cracks password in quite fast time if you have a good computer with fast RAM and processor. In backtrack 5 its already installed an is properly configured but you can get it on Ubuntu and other Linux flavours also. After installing Fern in any linux or else you can also use backtrack 5 for this purpose. Whatever OS you are going to use just run Fern and read below.
Using Fern Wifi Cracker:-
Click the refresh button to load monitor interfaces. Then hit scan button, its for dual functioning mean, at first hit it will start scanning and again if you hit it it will stop scanning.

Cracking WEP encryption based WIFI password key:-
After hitting the activation button of the WEP attack. What happens can be seen in screen shots below:-
So, key has been successfully recovered.
Cracking WPA encryption based WIFI password key:-
So, key has been successfully recovered, as you can see.
