DonCaron:
Something else just occurred to me. Game Mouses may be a problem.
I use it on my other steam games with no issue though.
Settings for the mouse are stored outside the game. I have used many different mice(both corded and wireless)for years with Steam, never had a problem.
Kinda makes me wonder tho, why all the questions and the game is not even there yet.
I can give you a couple of examples of cheat software that Steam will catch; Those that game will know what I am talking about. Even in single player you used to be able to open a console and type in different instructions(god mode, all ammo, etc.) Steam now disallows that on any game, it will not ban you but will stop scoring any games levels after you do so. I don't believe you want to do that in a multiplayer game, you might have to ask yourself, why can I no longer play.
Another big cheat in FPS was, be running with a sniper rifle and shoot a single shot in a opponents head. Only cheat software would allow you to do that and Steam will catch it.
You may also find yourself having to install some software, or you won't to able to get into multiplayer. Punkbuster used to be one that needed to be installed or you couldn't play multiplayer. Punkbuster is/was a cheat catching program, they are way beyond that now. The magic 7 iron would have been caught in a heartbeat.