Avira AntiVir Free created folders CONFIG, EVENTDB, INFECTED, LOGFILES, REPORTS, TEMP into my C:\ root. Had some error while trying to update (something to do with events/schedules), also.
Then I rebooted and updates worked normally.
Those folders (and it's files like scan results & logs) should go/be under %CommonAppData%\Avira\AntiVir Desktop. Those same folders are also in that path, and I could delete the new/weird ones from root/C:\.
Edit. After booting I deleted the folders, updated and ran some scans and the folders didn't reappear to the root anymore.