Yes you can play on multiple pc's, but only on LAN. And keygens will not work, nor will the ones on a google search, as the servers will kick you out. Even empty ones. my friends said about pirated and I tried the google search. I play LAN with my friend, and he brings his pc with a pirated code. If you do find a solution tell it to the world XD
PS: Moderators delete this post if i am breaking the rules, as i think im on thin ice here.