For a while, CCleaner was a trusted addition to anyone's cybersecurity arsenal. Recently, however, Microsoft marked CCleaner as a potentially unwanted application (PUA) for its Windows Defender antivirus.

Let's explore why Microsoft made this decision and what it means for you.

Why Windows Defender Now Labels CCleaner as a PUA

This isn't the first time that CCleaner has made the news for the wrong reasons. In our article on why CCleaner isn't safe, we cover some of the past scandals that arose with the program.

CCleaner had a tendency to install updates for itself without telling users, as well as monitoring what users were doing. Even worse, the software did the opposite of its job after a hacker used it to spread malware.

Despite this troubled history, however, this isn't the reason Microsoft has taken action. The company did ban links to it from its forums, stating that it believed registry editors did more harm than good. This recent marking as a PUA, however, is due to how the free version of CCleaner works.

In a statement to Bleeping Computer, Microsoft said:

"Our potentially unwanted application protection aims to safeguard user productivity. We detect instances anytime software offers to install other software that is not developed by the same entity or not required for the software to run, no matter the third party."

The free version of CCleaner comes bundled with third-party programs, thus matching Microsoft's definition of a PUA.

Should You Continue Using CCleaner?

If your Windows Defender flags your copy of CCleaner as a PUA, you can still continue to use it. It's not malicious and it won't install malware on your computer; it will just try to sell you third-party products.

However, given the app's shady history, you may want to move away from using CCleaner anyway. Instead of trying to make CCleaner work with Windows, you might be better off finding a replacement. In fact, in our guide to the best way to clean Windows 10, we use tools that come pre-installed with every copy of the operating system.

Getting More Out of Windows Defender

Windows Defender now flags CCleaner as a potentially unwanted program due to it showing ads for third-party software. If you go to install the free version and Windows Defender stops it, now you know why.

Update: Piriform has informed us that it's "in the process of engaging with Microsoft to understand why CCleaner was recently detected as PUA." The company surmises that the issue is "around bundling," and states that "we believe we have addressed this so that our product is now no longer flagged."

If you want to enhance your computer's PUA-detecting skills, be sure to learn how to block third-party junk offers with Windows Defender.