Steam proprietor Valve Software has apologised after its cheat-detection software banned over twelve thousand innocent Call of Duty: Modern Warfare 2 players.

Non-cheating gamers were flagged as cheaters by a mistake with the Valve Anti-Cheat feature of Valve's Steamworks suite, which Modern Warfare 2 uses. "The problem was that Steam would fail a signature check between the disk version of a DLL and a latent memory version," Valve president Gabe Newell wrote in an e-mail to the victims.

"This was caused by a combination of conditions occurring while Steam was updating the disk image of a game. This wasn't a game-specific mistake," he explained. "Steam allows us to manage and reverse these erroneous bans (about 12,000 erroneous bans over two weeks)."

"This was our mistake, and I apologize for any frustration or angst it may have caused you," wrote Newell. Valve has granted those mistakenly banned a free copy of Left 4 Dead 2 to gift to a chum plus a free copy for themselves if they didn't already own it.

Thanks to the many, many people who sent in tips on the subject.