When the Left 4 Dead demo went live for pre-order customers on Thursday, some very shrewd gamers figured out how to hack the PC version to allow split-screen co-op, play as the zombies, and use custom maps. Unfortunately, the fun's now over - Valve just closed the loopholes.

The demo will be opened up to the public on Tuesday so a patch was released on Steam today to correct a few lingering issues. On the patch notes, it specifically mentions that "fixes for demo exploits" were included. Boo-urns, Valve.

Even though you won't be able to battle zombies on your favorite Counter-Strike map anymore, the demo's still very fun and should have you chomping at the bit for the full game. Left 4 Dead will be released November 18th for Xbox 360 and PC.