I run Norton 360 antivirus on my PC.
It prompted me to run Norton Power Eraser (NPR) today
https://support.norton.com/sp/en/au/home/current/solutions/kb20100824120155EN_EndUserProfile_en_us to remove malware from my PC.
Norton Power Eraser identified (and deleted) JRiver Media Center 20.exe and two associated .dll files.
Norton's response was "11:06 AM Darshan Jain: Okay, that is fine, if Norton Power eraser removes any file or program then it means it has some threats on that program."
So now I have to download and reinstall MC20 on my PC, as well as rebuilding my library and changes I have made to the skin, font size and so on.
Which is a major pain in the backside.
I'm posting here so the administrators can get to the root of the problem and hopefully others won't have to go through this.