Left 4 Dea is an upcoming multiplayer co-operative survival horror FPS game by Turtle Rock Studios which is, as of January 10, 2008, part of Valve Corporation. The game has been built using Valve's Source engine and will be available on PC and Xbox 360. Certain Affinity is responsible for the Xbox 360 version of the game. Left 4 Dead puts four human playable or AI controlled survivors of an apocalyptic pandemic against hordes of the Infected. Regular Infected are controlled by the game AI, while human players can control up to four mutated Boss Infected with special abilities. The goal of Left 4 Dead for the Survivors is to help each other make it through a level to safety. Infected players must cooperate to stop them.