The Crysis 2 game requires a cd key to install and play the multiplayer mode online and that key is located on the user manual that's included in the case. On the rear of the manual at the top is the key code and this needs to be entered when it calls for it. As it states in the user manual in the online segment it is limited to one user per key code.
To play the campaign mode the key is not needed and the game can be installed on a few computers under the same EA account , you just need to download the EA game manager.
I have the game manual in my hand and that's what it says , I also installed the game and didn't play online right away and the key code was not asked for , it wasn't untill I went to play online that I had to register the key code to my account.