Call of Duty: Black Ops 2 is a futuristic take on warfare, but not quite this futuristic. Scattered buyers from all around the gaming community have claimed that in their PC copies of Black Ops 2, the second disc actually contains Mass Effect 2 data.
Players have talked about the problem on Reddit, Steam, and the Call of Duty forum (via Eurogamer), among others. The disc appears as it should, like a Black Ops 2 disc, but inserting it during the install process reveals its data as belonging to Mass Effect 2.
It's unknown how widespread this issue is, but it seems to be impacting PC copies only. This means affected users can't finish the install process for the game.
Obviously, Activision wouldn't have intentionally included data from an Electronic Arts game, so this problem probably stems from the production line. Shacknews has contacted Activision and will update as more information becomes available.