Okay, according to Destructoid at least, Modern Warfare 2 on Xbox 360 multiplayer has a problem that can, "'infect' your profile and turn you into the game equivalent of an HIV carrier." It apparently began via a PC mod.The story carried information based on "reports (that) players get 'infected' by unwittingly joining a private match hosted by a carrier. They then get hit by the same issue -- unlimited ammo and no reloads -- and can pass it on if the end up hosting any games themselves. Allegedly, it's 'spreading like an STD.'"
Infinity Ward is apparently working on it - and Microsoft is banning anybody who uses it.