Description

 Follow these steps.
1. Make sure to patch your pirated mw2 to the latest patch (1.0.175 currently).
In steam, go to your friends section and set your status to offline.
2. Start mw2, and play free-for-all (easiest to find a working game to play in).
3. Press the hotkey to open steam overlay (default is alt+tab I believe), 
and click on status, then hover your mouse over "offline." 
As soon as mw2 finds an open game (will say "1/2" "1/4" etc), click on offline, 
to immediately set your status as offline again. If you do not, as soon as mw2 finds an open 
game, you will get the "disconnected from steam" error again.
4. When the game is over, do the same thing again - set your status to offline 
immediately when the game ends.