Robert Bowling (fourzerotwo) just tweeted that the Call of Duty 4 Title Update for Xbox 360 is now Hack and Mod free. Not that I personally came across this (maybe) but at least I will not now. If you are unfamiliar Call of Duty: World at War had the same similar update last week in its update to fix the same thing going on with hacks and mods there too.
Source: Twitter