To start with a description for my Question:
In that short Manual that is delivered with the Game, you can find a sentence that tells you to be able to play CoD:MW3 online or local.
The only reason why I bought this game was this sentence (I played many Games most times on LAN's, often without an Internet-Connection).
The last Games (after Crysis and Crysis Wars, CoD 4/5 and UT3) are only playable with others in online-Multiplayer Matches.
I thought at least Activision would bring out a Game that would be playable in local Network like it is possible with the Games listed above and older ones.
After installing the Game together with STEAM for the Activation of the Game I hoped this will be all that is needed (online Activation is an acceptable way of handling the problems of illegal Download and crack-using).
But the biggest problem showed up right after starting the Game the second time (first time was simply for testing and setup).
I switched off STEAM (offline-Mode) and tried to run the Multiplayer.
The only message you get is that STEAM has to be online for using Multiplayer-Mode.

And now to add another Question to my topic Question:
Why is Activision writing, that this Game can be played also in local Multiplayer, when you have STEAM to be online?
(ok, on technical view it is only STEAM that needs a connection to Internet, but it blocks the complete Multiplayer-functionality of this Game. It would be enough if only the Online-Multiplayer Part wouldn't work, what makes sense if not being able to connect to Internet / STEAM)

I hope this issue will be corrected with a Patch

EDIT (11.12.2011):
That's great, still no answer after two weeks.

I'm happy that CoD2, CoD4, Crysis Wars and UT3 are still playable on LAN (local Multiplayer)

Message was edited by: RaptorXP