@Michel0079 Turning of your F-Secure is ofcourse not the best solution .
I also use F-Secure and had the same problem after the latest update.
You can exclude the file DCS_updater.exe file in the deepguard part of F-Secure. That way, F-Secure remains active, but the DCS_updater.exe file, which is used to start DCS, is no longer scanned and DCS starts without any problem.
This is for the standalone version of DCS, so I don't know if this will work for the Steam edition too.