In Ubuntu, just open a terminal window and install macchanger if needed..

sudo apt-get install macchanger

OK, now use macchanger..

sudo macchanger eth1 -r

This will change the wifi address, as your physical CAT 5 port is prolly eth0. The command above will change the MAC address to a random MAC address.

If you need to find out what the name of your ethernet ports are, including wireless, look no further…

sudo ifconfig

Sweet!