Celebrating Halloween in cooperative undead slaughtering style, Valve has announced Left 4 Dead 2 will be free to download and play this weekend, commencing tomorrow.

To celebrate Halloween, we are unleashing L4D2 on the world. Starting this Thursday, the entire game will be free to play for the whole weekend. New players can begin pre-loading now. For long time players, it is time to welcome your new found friends and help them survive the zombie apocalypse.

For current players, we created a new achievement. Good Guy Nick - – “Plays games with free weekend players and helps them survive a campaign.” Who is a free weekend player? You’re going to have to talk to each other to find out or you could always let your friends know Left 4 Dead 2 is going to be free this weekend and have them join you. Spread the word! It’s the zombie apocalypse, bring friends.

Curious players that don't already own the game can start pre-loading from in anticipation with this link.

The promotion commences on October 5th PDT (exact time uncertain), and winds up on October 29th 10am PDT, which equates to a local Sydney start time sometime after 6pm AEDT Friday, and finishing at 4am AEDT Tuesday.