The InfinityWard.com forums are receiving warnings from users that they are experiencing issues where they are having trojans interjected into their machine when joining certain IWNet games.Users have been quick to point the figure that a clan has possibly hacked the game DLL files are injecting the trojans using a combination of those files and open ports on the guest clients end.This issue is currently receiving mixed reports, we recommend strongly that you use antivirus (like AVG).If you don’t have an antivirus yet, you can download one legally for free at http://free.avg.com/ or at http://www.free-av.com/ has reported that they believe this to be a false positive, http://www.mapmodnews.com/article.php/MW2-AVIRA-Crypt.XPACK.Gen-Trojan.
More information regarding this Trojan spreading trough IWnet can be found here:
http://www.infinityward.com/forum/viewtopic.php?f=24&t=181730
http://www.infinityward.com/forum/viewtopic.php?f=24&t=181646
http://forums.steampowered.com/forums/showthread.php?t=1031092Update
http://www.mapmodnews.com/article.php/MW2-AVIRA-Crypt.XPACK.Gen-Trojan
http://www.infinityward.com/forum/viewtopic.php?f=24&t=182082