An epic bug hunt featuring a unique blend of co-op play and squad-level tactics. With your friends, form a squad of four distinct IAF Marine classes. Plan your attack using an unlockable arsenal of weapons with countless loadout configurations against a wide variety of aliens. Blaze your way through an overrun, off-world colony, eradicating the alien infestation in environments ranging from the icy planet's surface, to a subterranean lava-flooded mining facility.
A small campaign for Alien Swarm. Your secret mountain lab has been attacked by aliens. The chopper that should fly you out crashed. Now you have to make your way down the mountain, through the facility... which is infested by alines.
Download, extract, doubleclick the vpk file