Fancy a free game? Head over to the Steam store and click the “Install Game” button. Overkill is giving free five million copies of the game on Steam on a first-come-first-served basis, so be sure to claim the deal before its over!
Once you click the Install Game button, the game is registered to your account permanently. Be sure to claim it, otherwise it will go back to its original price when all five million copies are claimed!
Interested peeps head here for claiming the game for free :