CCleaner detected as a PUA by Microsoft’s antivirus

Jul 30, 2020 06:47 GMT  ·  By

CCleaner is now flagged as a Potentially Unwanted Application, or PUA, by Microsoft’s Windows Defender antivirus, and its installation is thus blocked on Windows 10 devices.

While the software originally added CCleaner to its threat database with only a few details, Microsoft published an update on July 29 to explain why exactly the application is blocked by Windows Defender.

Microsoft says CCleaner itself is not a dangerous program but its installer includes certain software, such as Google Chrome, the Google Toolbar, Avast and AVG antivirus that users may not want.

“Certain installers for free and 14-day trial versions of CCleaner come with bundled applications, including applications that are not required by CCleaner or produced by the same publisher Piriform. While the bundled applications themselves are legitimate, bundling of software, especially products from other providers, can result in unexpected software activity that can negatively impact user experiences,” Microsoft says.

CCleaner installation blocked

These are all clean apps, Microsoft emphasizes, and despite the CCleaner installer offering a setting to opt out and prevent them from downloading and installing, some users might not necessarily spot these options and end up running software they didn’t ask for in the first place.

“Some installers for the free version of CCleaner, also based on Nullsoft, include an installer for Google Chrome with the file name PF-Chrome-2019.exe. After installing Google Chrome, the installer sets the bundled application as the default web browser. Some variants of the same installer also add the Google Toolbar to Chrome as an extension,” Microsoft says.

As a result, Windows Defender just blocks CCleaner completely, as long as the installer itself comes with such software bundled by default. On the other hand, worth knowing is that not all installers are blocked, as Piriform, the Avast-owned maker of CCleaner, is also offering separate packages that come without any other programs offered to users during the installation.