Big money selling free computer games

Video game producers have been accused of many things, from greediness to promoting Satanism, so it was a surprise yesterday when software development company Valve released a new, professionally-made game free of charge. That's right, Alien Swarm (a top-down, cooperative shooting game) is available to play for the click of a button. To really shock and amaze, Valve also released the full source code for others to emulate or modify.