Alien Swarm is a free video game that combines cooperative play and squad-level tactics in an epic bug hunt. Players form squads of four IAF Marine classes, and use unlockable weapons with different loadout configurations to fight a variety of aliens. They must battle through environments like icy planets and lava-flooded mining facilities to eradicate the alien infestation. Along with the game comes access to the complete code base for Alien Swarm, which has updates to the Source engine as well as 3rd person camera, depth of field, improved dynamic shadows and other gameplay additions.