Microsoft Flags CCleaner as Potentially Unwanted Application, Deletes Its Files

CCleaner, one of the most popular cleaning and system optimizations app for Windows, is now detected as a potentially unwanted application, or PUA, by Microsoft’s antivirus engine.

While CCleaner has previously been accustomed to spread malware after hackers managed to inject malware into its installer, this doesn’t appear to be the reason for Microsoft flagging the most recent version of the app as PUA.

Microsoft explains in its threat database that CCleaner is now detected as PUA:Win32/CCleaner by the Windows Defender Antivirus, with all of files automatically removed from Windows computers. The CCleaner listing was last updated on July 27.

While Microsoft hasn’t provided any information why the app is now flagged like a PUA, it’s not a secret that the software giant itself isn’t a big fan of such cleaning apps.

In a support document, the company explains that embracing such apps can eventually affect the stability of Windows.

“Some products for example registry cleaning utilities suggest that the registry needs regular maintenance or cleaning. However, serious issues can occur whenever you customize the registry incorrectly with such types of utilities. These problems may need users to reinstall the operating-system because of instability. Microsoft cannot be certain that these complaints could be solved with no reinstallation of the Operating System because the extent from the changes produced by registry cleaning utilities differs from application to application,” it says.

Microsoft recommends against using CCleaner

Back in October 2015, only a few months after officially launching Windows 10, Microsoft recommended against using CCleaner.

Gov Maharaj, Principal Software Development Engineer at Microsoft, explained that users should rather avoid installing CCleaner on their own devices, all without providing too many specifics on the actual reason.

“CCleaner is… how do you put it mildly… Don’t… let’s just move on!” he explained.

We’ve reached to Microsoft for more information on the CCleaner listing and can update the content when and when we hear back.

Update: Microsoft has updated the threat database with increased info on why it blocked CCleaner.