Alien Swarm Unlocks Special Hat in TF2

Completing two online co-op campaigns in Alien Swarm, nets you this hat drop in Team Fortress 2–reportedly, the first time Valve has done something like this. And, since Alien Swarm is free, there’s no reason you shouldn’t be playing it, anyway. The only prerequisite is that you have TF2, and who doesn’t have that game?