CD Key

Your CoD CD key is a number located inside your CoD CD case that is provided by
activision. This CD key is checked everytime you enter a CoD multiplayer server. Sharing
CD keys with another player might make it so you will recieve a message when you try to
enter game saying "Error CD Key in use" or something like that. In most cases if you wait
5 or so minutes it will stop doing that.

A new CD key can be entered in the "Multiplayer Options" section of the main menu.
There may be an easier way to view this, but in order to find my current CD key i do the following. Click start on your desktop taskbar > Go To "Run" > Type in "regedit" > HKEY_LOCAL_MACHINE > SOFTWARE > Activision > Call of Duty > codkey. You can
copy paste it if you want, or just view it.

Your CD key also provides your guid, which is your id number for multiplayer CoD.
This is what gets banned from servers, so even if you give your CD key away, it will have
the same guid and be banned from the same servers.