As many as four million copies of the PC shooter Crysis 2 had been pirated online last year, new data suggests.
The Crytek title was the most illicitly downloaded game of 2011, according to data published by TorrentFreak, with about 3,920,000 copies pirated since its release in March 2011.
Modern Warfare 3 followed close behind in the rankings with 3,650,000 copies taken.
Battlefield 3 (3,510,000) came third, ahead of FIFA 12 (3,390,000) and Portal 2 (3,240,000).
Together, these five games constituted about 18 million illicit downloads.
The unconfirmed data is based on torrent usage, and has not been corroborated by the publishers nor the developers of the games.
Nintendo Wii games were the most downloaded of all the consoles, the figures suggested.
Super Mario Galaxy 2 was struck by 1,280,000 illegal downloads, some 400,000 more than the most pirated Xbox game, Gears of War 3.
Wii games are relatively smaller in file size than both PlayStation and Xbox, and the system is regarded in some circles as a soft target for games piracy.