Avast put this undeletable folder/file in my data drive. Sucks.
Only way I could remove it was to uninstall Avast, then delete it. Then installed Avast.
Tried cmd prompt at admin level, hidden admin account, pause shields, empty quarantine - nothing worked. Lots of web entries but no actual solutions!
Note: I don't give a hoot if the emptied "vault" is benign! It's protected status kills backups and maintenance! I HATE it!