For a while, CCleaner was a trusted addition to anyone’s cybersecurity arsenal. Recently, however, Microsoft has made a surprising move and 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.