Enviroment - Windows 10 Home, Version 1803, Laptop
During the day on Christmas Eve I was playing a game that was launched by a file DoctorWho_Pc.exe via a shortcut on my desktop. The game has been on my PC for quite a while and was reinstalled several months ago when I had a system crash, all with no problems. I launched the game several times during the day again with no problems. However, on Christmas Day, when I wanted to play the game for a short while before I went out I was told that the shortcut pointed to a file that was either missing or had been moved. I tried restoring the exe file from a backup and that failed. Restoring to a different location and then trying to copy to the original location failed with permission errors. Having tried various solutions to the permissions problem that I had googled to no avail, I uninstalled the game and tried to reinstall it and I got a write error on the exe file and it wouldn't reinstall. At this point I was at a loss as to what to try next and I contacted the developers.
This morning, before I had a reply from the developers, I suddenly had the thought that I wonder if Avast had done something with file. When I checked the vault, there was my exe file. When I restored it I could then do a reinstall of the game which got it working again.
What I don't understand is the following:-
1. How can a file that has been on my computer for several months (and been accessed in that time) suddenly be flagged as a virus?
2. How was it that I managed to play the game for over an hour with no problem only to find that the file had been quarantined (as I now know) when I shut the machine down.
3. Why was there no warning that a file I had been using had a suspected virus and was about to be quarantined? This woul have certainly saved me a lot of grief and hard work trying to work out what the problem was with the game.