F-Secure incompatibility with Steam gaming platform (cannot play games)
So this has been a very longstanding issue which I have been in contact both with Steam Support and F-Secure and there is still no solution to the problem.
You cannot play a lot of the games on Steam if you have F-Secure installed, you just get an error in Steam when you try to launch a game.
Here is the KB article on Steam Support about the issue:
Game failed to start (Error code 51)
F-Secure uses a feature called DeepGuard which may interfere with Steam. If you are seeing the above error, disable DeepGuard and re-test the issue. If the issue continues, you may need to *temporarily* uninstall F-Secure to determine the cause of the problem.
However there is no solution to the problem. Nothing works, not even turning F-Secure off in its settings.
I have no idea what to do but to put this up here in the forums.