Here is the final analysis:
- there is definitely no Virus or so, these false positives can be ignored
- there is a bug in LyX we need to fix:
- I created a new installer that forces a silent MiKTeX update. This
assures that every user gets the current MiKTeX package handling system.
- there are 2 bugs in MiKTeX that make problems:
* this one is already fixed but the fix it not yet published (only few
user will be affected):
* this one causes the problem LyX users reported (everyone will be
affected who had MiKTeX already installed before installing LyX 2.3.0):
- Conclusion: I cannot do more right now to wait until MiKTeX releases
the fixes for the 2 bugs.
Sorry and regards