You may distribute your modified Valve game in source and object code form, but only for free.'
^ AlienSwarmArchived at the Wayback Machinefork on 'readme: You may, free of charge, download and use the SDK to develop a modified Valve game running on the Source engine.^ Alien Swarm with complete code base releasing FREE on SteamArchived at the Wayback Machine on Gameranx (July 16, 2010).^ 'Alien Swarm Game & Source SDK Release Coming Monday'.'Valve To Freely Release Source-Powered Alien Swarm, Entire Codebase'. 'The Best of 2004 The 14th Annual Computer Games Awards'. ^ GameSpy Mod of the Year 2004Archived at the Wayback Machine.'Valve Unleashes An Alien Swarm On Steam'. 'Free Alien Swarm Game Is So Much Fun, It's Almost Unreal (Tournament)'. ^ a b c Sterling, Jim (July 26, 2010).