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 used to spread malware after hackers managed to inject malware into its installer, this doesn’t seem to be the reason for Microsoft flagging the latest 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 files automatically removed from Windows computers. The CCleaner listing was last updated on July 27.

While Microsoft hasn’t provided any information as to why the app is now flagged as 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 turning to such apps can eventually affect the stability of Windows.

“Some products such as registry cleaning utilities suggest that the registry needs regular maintenance or cleaning.  However, serious issues can occur when you modify the registry incorrectly using these types of utilities. These issues might require users to reinstall the operating system due to instability. Microsoft cannot guarantee that these problems can be solved without a reinstallation of the Operating System as the extent of the changes made by registry cleaning utilities varies 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 devices, all without providing too many specifics on the actual reason.

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

We’ve reached out to Microsoft for more information on the CCleaner listing and will update the article when and if we hear back.

Update: Microsoft has updated the threat database with more information on why it blocked CCleaner.