Microsoft apparently doesn't want you to install CCleaner on Windows 10, as Bleeping Computer discovered that Windows 10's built-in antivirus software, Windows Defender, flags users who try to install this software as Bleeping Computer discovered that Windows 10's built-in antivirus, Windows Defender, flags users who attempt to install this software as "potentially undesirable software.

"Potentially undesirable software" - sometimes known as "potentially undesirable apps" or PUAs - is not flagged as malware or malicious. However, they are potentially annoying.

Microsoft's explanation seems to confirm this.

"The installer for the free or 14-day trial version of CCleaner contains bundled applications, including applications that CCleaner does not require and applications created by the same Piriform company.

Bundled applications include Google Chrome, Google Toolbar, Avast Free Antivirus, and AVG Antivirus Free. Avast owns Piriform, the publisher of AVG and CCleaner.

"While the bundled applications themselves are legitimate, bundling software, especially products from other providers, can cause unexpected software behavior and negatively impact the user experience," Microsoft concluded, justifying this flag.

This certainly won't help software still suffering from past reputational damage; a Google search reveals a number of questions in the "People also ask" section that the company doesn't necessarily seem pleased with:

The malware and The "infected" question relates to a malicious version of CCleaner released in 2017, in which hackers managed to insert code to steal data from users. There were also rumors in 2019 that Microsoft was planning to include a link to the site in its own community forum blocklist, fearing that enthusiastic amateurs would do more harm than good with the registry cleaner's power.

Still, the company is confident that this latest issue with Windows 10 will be short-lived.

"We are in the process of engaging with Microsoft to understand why CCleaner was recently detected as a PUA," a CCleaner spokesperson told TechRadar. We speculate that the issue is related to bundling."