Valve's anti-cheat technology ran amok over the past couple of weeks and started banning Modern Warfare 2
players for no reason. Valve has now corrected the problem, and has un-banned these players. To compensate, they are offering a free copy of Left 4 Dead 2 to play and another to gift to a friend. A letter from Valve's Gabe Newell reproduced on Kotaku
explains the problem, and the L4D2 deal: "We have reversed the ban, restoring your access to the game. In addition, we have given you a free copy of Left 4 Dead 2 to give as a gift on Steam, plus a free copy for yourself if you didn't already own the game."