Windows 10 is warning users not to install CCleaner

Piriform CCleaner
(Image credit: Shutterstock/Piriform)

CCleaner, a popular PC optimization app, is being flagged up as ‘potentially unwanted software’ by Microsoft Defender (formerly Windows Defender, but renamed with the May 2020 Update), which is Microsoft’s built-in antivirus for Windows 10.

Potentially unwanted software – more commonly referred to as potentially unwanted apps (or PUAs) – refers to applications which an antivirus doesn’t find anything malicious with, but which may exhibit unwanted behaviors of one kind or another.

Usually, that means bundling extra bits and pieces, or stealthily installing extras like, say, a browser add-on, which may not do your PC any harm, but could prove an annoyance.

As Bleeping Computer spotted, Defender now detects CCleaner as a PUA, with the software giant stating that: “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.”

Avast extras

Those bundled apps include Google Chrome browser, Google Toolbar, and Avast Free Antivirus plus AVG Antivirus Free (note that Piriform is now owned by Avast, which also owns AVG too).

Microsoft further stresses that those bundled apps are perfectly fine and not in any way malicious, of course, but it’s the way that they are offered for installation which is problematic.

The company observes that while the CCleaner installation process does provide a way to opt out of putting these extras on your PC, as you would expect, the judgment is that “some users can easily inadvertently install these bundled applications”.

Often, these matters are down to the way the options to opt out are presented.

At any rate, according to a statement just released by CCleaner, the firm believes that the issue has been resolved.

A CCleaner spokesperson told us: “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.”

So, it may now be the case that if you go to install CCleaner while running Microsoft Defender, you’re no longer warned against proceeding, assuming the security app is indeed updated as CCleaner asserts.

Darren is a freelancer writing news and features for TechRadar (and occasionally T3) across a broad range of computing topics including CPUs, GPUs, various other hardware, VPNs, antivirus and more. He has written about tech for the best part of three decades, and writes books in his spare time (his debut novel - 'I Know What You Did Last Supper' - was published by Hachette UK in 2013).

Read more
Windows 11 working on a laptop PC
Windows 11 PC slow or low on storage? Bloatware could be to blame - here's how to find and remove it
Phone scammer
Microsoft thinks it could stop this dangerous scam forever
Young woman using laptop, looking annoyed
Microsoft’s latest bit of nagging in Windows 11 might come from a good place, but it’s seriously annoying some people
AI PC laptop
Best PC cleaner of 2025
A woman sitting in a chair looking at a Windows 11 laptop
Windows 11 fully streamlined in just two clicks? Talon utility promises to rip all the bloatware out of Microsoft’s OS in a hassle-free way
Man having Windows 11 problems with his laptop
Fed up of adverts creeping into Windows 11? You won’t like Microsoft’s latest update, then, although it does provide some important bug fixes
Latest in Windows
Using Zipped files and folders in Windows 11
Windows 11 should soon be faster at extracting files from compressed ZIPs – and it’s about time, frankly
Xbox Wireless Controller
Microsoft is adding a powerful new feature for using Xbox controllers with Windows 11
Woman disgusted by her laptop
Embarrassing Windows 11 bug that deleted Copilot app is now fixed – but will anyone outside of Microsoft care?
Student sat at a desk with a laptop in a dormitory looking at a mobile phone
Windows 11 could eventually help you understand how fast your PC is - as well as offer tips for making your PC or laptop faster for free
Windows 10
Microsoft gets into the spam game by again emailing Windows 10 users to prod them to upgrade to Windows 11 – is the nagging going too far now?
Using Zipped files and folders in Windows 11
Hidden clues suggest Microsoft is moving another part of Windows 11’s Control Panel to the Settings app – and this time it’s mouse options
Latest in News
Quordle on a smartphone held in a hand
Quordle hints and answers for Sunday, March 23 (game #1154)
NYT Strands homescreen on a mobile phone screen, on a light blue background
NYT Strands hints and answers for Sunday, March 23 (game #385)
NYT Connections homescreen on a phone, on a purple background
NYT Connections hints and answers for Sunday, March 23 (game #651)
Google Pixel 9 Pro Fold main display opened
Apple is rumored to be prioritizing battery life on the foldable iPhone – which could also feature a liquid metal hinge for added durability
Google Pixel 9
The Google Pixel 10 just showed up in Android code – and may come with a useful speed boost
L-mount alliance
Sirui joins L-Mount Alliance to deliver its superb budget lenses for Leica, DJI, Sigma and Panasonic cameras