Go to the computer, and type in "Zork", you'll get an achievement and a word based game. You may want to look up, or ask somebody how to play it, because it's kinda weird to explain. You give commands like "get" "open" north" etc. to win. It's a word based adventure game. I tried to download it, but I can't play it, because my computer is too new for it.
I know what zork is, but you said "I'm playing Zork on CoD: BO". Like it was hidden on the disc or something.
Speaking of Zork, the first videogame I played (and beat) when I was a little kid was the original Adventure Colossal Cave. I don't think I ever got to into the zorks, but I did beat most of the infocom text adventures.
You can play it, but some parts are unbeatable because you can't use quotation marks and such. You get an achievement for booting it up on the computer though.
Omni- at the main menu look.down at your hands un the chair, alternate the triggers a bit and you break out. In the room there is a computer you can access. Type" zork" into it and boom your in. also type "doa" for another hidden game.