After running scans, which in fact did find and isolated some malware, I tried again. And again after some time the Runtime broker went sky high up.
With my own account was nothing wrong.
Conclusion: the fail was local to the account, Windows was stil undammaged.
I backed up and removed completely that damaged account, than I recreated it, to be on the save side I used a different account name, followed by restoring the backuped data.
Job done, problem solved