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.

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