From a computer magazin's webside a downloaded a windows repair tool and got an additional game and computer cleaner software, Iobit Advanced SystemCare 11.
Uninstalling using the windows system was not very successful, obviously the visible icons were deleted, but not the program itself.
A scan with AdwCleaner showed residual files, but when trying to delete AdwCleaner stop working with an Unhandled Exception.
In a next step I used the program Unlocker to get rid of those files. But this was only possible after killing some associated processes (with the help of Unlocker) and some restarts.
After deleting all files in question manually with the help of Unlocker, it was possible to start AdwCleaner again to handle the registry entries.
This time AdwCleaner worked as fine as ever.