Unused file extensions not unused? in CCleaner Posted February 18, 2011 Just out of curiosity I ran the latest version of CCleaner today 3.03.1366 on my XP PC. Using the Registry section and "Scan for Issues" it seems to be detected a lot of "unused" file extensions, however I beg to differ. When double clicking on the files containing the above extensions they launch their default assigned application. These extensions are not unassigned so why does Ccleaner state that they are unused?? Richard S. Yes. And yes, again. Be very careful. I cannot use the "unused" file extension part of the program. It would destroy many files associated with my (many) applications. I think CCleaner only recognizes some file extensions and so thinks anything not in its database is invalid. Mostly I stay away from the registry cleaner as it has caused me problems. I run the scan. If I know EXACTLY what something is AND that it is safe to get rid of it, MAYBE it gets deleted, and then, ONLY after I have backed up the registry.