Windows Defender bug causing Quick and Full scans to fail

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Microsoft confirmed that manual and scheduled scans with Windows Defender are impacted by a bug.

Windows Defender

What you need to know

  • The latest version of Windows Defender has a bug that causes Quick and Full scans to fail.
  • Real time scanning still works for Windows Defender despite the bug.
  • Microsoft confirmed that the company is working on a fix.

Windows Defender version 4.18.1908.7 was released earlier this week. The bug causing scans to fail was introduced while Microsoft attempted to fix a separate bug in the July 2019 Patch Tuesday update.

In addition to Windows Defender on Windows 10, the bug affects all versions of Windows Defender on all versions of Windows. As pointed out by ZDNet, the bug also affects Security Essentials.

Microsoft confirmed to ZDNet that the company is working on a fix for the bug. Microsoft pointed out that real-time scanning protection still works despite the bug and that malware should be detected in real-time.

If you'd like to scan your system while the bug is still affecting Windows Defender, you can still perform a Custom scan with the tool.

Sean Endicott
Sean Endicott
News Writer and apps editor

Sean Endicott is a news writer and apps editor for Windows Central with 11+ years of experience. A Nottingham Trent journalism graduate, Sean has covered the industry’s arc from the Lumia era to the launch of Windows 11 and generative AI. Having started at Thrifter, he uses his expertise in price tracking to help readers find genuine hardware value.

Beyond tech news, Sean is a UK sports media pioneer. In 2017, he became one of the first to stream via smartphone and is an expert in AP Capture systems. A tech-forward coach, he was named 2024 BAFA Youth Coach of the Year. He is focused on using technology—from AI to Clipchamp—to gain a practical edge.