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Windows 10 users shouldn't install this popular app, Microsoft says

(Image credit: Ccleaner)

Don't install CCleaner, Microsoft warns.

Microsoft Defender Antivirus, formerly known as Windows Defender, is flagging the popular junk-file remover as a "potentially unwanted program," Bleeping Computer reported (via our sister site Tom's Guide).

What is CCleaner?

CCleaner is a disk-cleaning app that's been around since 2004. It is owned by Piriform, a company Avast purchased in 2017. CCleaner claims to boosts PC performance  — improving speed, safety and security — by removing unwanted, space-consuming files.

Why is CCleaner being flagged by Microsoft Defender Antivirus?

Microsoft Defender Antivirus has it out for CCleaner. Why? According to the Redmond-based tech giant, CCleaner installers are often bundled with superfluous, needless applications — and Microsoft isn't having it.

"While the bundled applications themselves are legitimate," Microsoft wrote on its Security Intelligence blog, "bundling of software, especially products from other providers, can result in unexpected software activity that can negatively impact user experiences."

Software applications that are often bundled with CCleaner include Google Chrome, Google Toolbar, Avast Free Antivirus and AVG Antivirus Free. Microsoft added that while the CCleaner installer offers users the option to opt-out of unnecessary software, many Windows users end up inadvertently installing the programs.

In order to "protect" Windows users, Microsoft Defender Antivirus flags CCleaner as a potentially unwanted application (PUA). 

CCleaner's rocky history with Microsoft

Piriform and Microsoft haven't had the best relationship. In the fall of 2019, the Redmond-based tech giant censored CCleaner from its support forums to block members from recommending the junk-file remover tool. Microsoft shortly backpedaled on this decision. It's unclear what caused Microsoft to blacklist CCleaner in the first place, but the conglomerate always had an aversion to registry cleaners.

"Microsoft does not support the use of registry cleaners. Some programs available for free on the internet might contain spyware, adware, or viruses. If you decide to install a registry cleaning utility, be sure to research the product and only download and install programs from publishers that you trust," Microsoft wrote in 2018.

In 2017, CCleaner suffered a loss of reputation; hackers injected malware into the legitimate application to steal data from users. With CCleaner trying to clean up its image as an authentic program over the years, Microsoft Defender Antivirus isn't helping by flagging the disk-cleaning software as a PUA.

“We are in the process of engaging with Microsoft to understand why CCleaner was recently detected as PUA. We surmise the issue appears to be around bundling, and we believe we have addressed this so that our product is now no longer flagged," a CCleaner spokesperson told TechRadar.

With Google apps being included in CCleaner's bundles, we can't help but wonder if Microsoft is only penalizing CCleaner to stifle one of its biggest competitors.