Black Ops 2 – some of the same people who waited in line for hours on a cold November night during the midnight launch – popped in the second installation disc to find that it's for Mass Effect 2. Reports on Steam, Reddit, 4chan and the Black Ops 2 forums describe the same problem, and the video below shows it in action (along with some NSFW language).
This prevents these players from installing Black Ops 2 with the discs, but each retail copy comes with a Steam key and the entire game can be installed digitally. It will take a while, but it is at least, eventually, playable; this process largely negates the entire "waiting in line for a retail version" thing, though.
We've contacted Activision for more information.