Microsoft Defender now flags CCleaner as a Potentially Unwanted app

CCleaner, a popular tweaker, system cleanup utility, and app removal tool is now flagged by Microsoft Defender Antivirus, similar to what had happened to Winaero Tweaker in the past. However, this time Microsoft explains why it is so.


CCleaner was initially developed by Piriform, which is a company acquired by Avast in 2017. The app is a utility used to clean potentially unwanted files and invalid Windows Registry entries from a computer. First launched in 2004, it remains very popular over years among Windows users.


Such unfortunate incidents had previously happened with the CCleaner app. Earlier, it was banned to post about it on the Microsoft Community forums since it was considered 'bad advice'.

There are a number of reasons for Microsoft to not like the app. It can be used to remove critical Registry entries,  apps, etc, so an inexperienced user can tweak the OS to work in some unexpected way. However, this is applicable to ANY of the tweakers available these days. These tools are for advanced users who know what to do, and are intended to save their time.

However, the official reason for today's change is expressed on the Microsoft Security Intelligence site, and it is all about software bundling. It says:

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. To protect Windows users, Microsoft Defender Antivirus detects CCleaner installers that exhibit this behavior as potentially unwanted applications (PUA).

The installers detected as PUA include CCleaner installers that have been found bundling the following applications. Note that these are normal applications that are not detected by Microsoft Defender Antivirus.

  • Google Chrome
  • Google Toolbar
  • Avast Free Antivirus
  • AVG Antivirus Free

While the CCleaner installers do provide an option to opt out, some users can easily inadvertently install these bundled applications.

One of the reasons may be that Microsoft may not be happy to have Windows 10 users inadvertently disabling Microsoft Defender after installing Avast or AVG antivirus solutions.

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Author: Sergey Tkachenko

Sergey Tkachenko is a software developer who started Winaero back in 2011. On this blog, Sergey is writing about everything connected to Microsoft, Windows and popular software. Follow him on Telegram, Twitter, and YouTube.

7 thoughts on “Microsoft Defender now flags CCleaner as a Potentially Unwanted app”

  1. At least Microsoft are doing something about the practice of bundling unnecessary software and the sneaky way they are inadvertently installed without user knowledge

    Well done Microsoft for taking a stand on this and hopefully forcing Avast to clean up their software of this malicious crap!

    For once Microsoft should be applauded and not condemned for their actions

    As its not often I praise Microsoft, but on this occasion I do!

  2. I done an upgrade from Win7 to Win10. Then my registered (and paid for) copy of CCleaner was uninstalled without any prompts or warnings. MS doesn’t like CCleaner because it can perform a solid job at bypassing Appwiz.cpl to remove programs that are corrupt/unable to unistall and it also does a wonderful job in cleaning the registry. This all stems from the fact that MS doesn’t like other people doing better work than themselves. CCleaner is an amazing program! Ccleaner has helped me countless times when other software couldn’t do what it did. This ‘flagging’ bullshit only shows how big of a bully MS really is.

  3. Agree with Zappa, as soon as Piriform started bundling unwanted and unnecessary crap with CCleaner, I switched to the portable version and have never looked back.

  4. Thank you Bob.
    Untill today MS did not even succeed in delivering Windows version 2004 to my pc. I am still waiting.

  5. Hi Guys,
    Forgive me If I am wrong but I seem to be having a bit of a hit or miss day for the last 2 weeks with this defender crap.[censored]

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