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.

The latest version of Windows Defender has a bug that will cause Quick and Full scans to fail after only a few seconds and scanning only a small number of files (via ZDNet). The bug affects Windows Defender version 4.18.1908.7 and later. Several users reported the issue on Microsoft support forums as well as Reddit.

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.

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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

Sean Endicott is a News Writer at Windows Central, where he covers Windows 11, Surface hardware, Microsoft 365, AI, apps, and the broader PC ecosystem. Since joining the site in 2017, he has written well over a thousand articles across the Microsoft landscape, covering breaking news, analysis, and feature reporting.

He writes Windows Wrap, a weekly column covering the biggest stories in Windows and the PC industry, and what they mean for the platform going forward.

Before joining Windows Central full-time, Sean worked in journalism and media production after earning a First Class degree in Broadcast Journalism from Nottingham Trent University. Outside of tech, he is an award-winning American football coach based in Nottingham, England, and was named BAFCA Youth Coach of the Year in 2024.