Some PC gamers have reported being unable to fully install Call of Duty: Black Ops 2 after discovering that the second game disc is in fact Mass Effect 2.

The bizarre manufacturing mix-up has been reported by gamers on Reddit, Steam forums and the Call of Duty forum.

Presumably the included CD Key can be used to activate on Steam and download the game, thus bypassing the need to install from DVDs. For gamers on limited broadband connections this won't, however, be possible.

Activision hasn't said how it plans to rectify the situation.