From my understanding it will add porn adverts to the PC. It starts itself on system boot.
"The tool creates an autorun entry for itself to run on system startup. When it is run, it creates porn pop ups, which cannot be closed with simple techniques. In addition, the taskmanager and registry editor are disabled. The file needs .NET to run."
It's not the end of the world, but I 100% don't want it on my machine. I've played and unwrapped dozens of Ren'Py games that didn't run into this issue. Maybe a Window's update is flagging them now? Python is a pretty easy langue to sneak in malicious stuff out on the open source side of things. Which Ren'py could be hit with as easily as anyone else.
What version of Ren'py are you using? I am seeing post around Windows make a false alarm on RenPy games which was build on 8.2.3 version. There are also some older hits on 7.x.x versions on reddit.