Nasty Windows 10 flaw breaks Windows Defender: Protect yourself now

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Microsoft has another Windows 10 update issue on its hands, and we've got the solution

Windows 10
(Image credit: ymgerman / Shutterstock)

Another day, another nasty Windows 10 flaw. Somehow, the latest Microsoft update is breaking Windows Defender, which could leave your system exposed if you're relying on Microsoft's built-in antivirus software.

Your system is affected if Windows Defender crashes whenever you try to run a full system scan. Fortunately, the folks at Bleeping Computer caught this bug and learned of a fix, which we've got below — and it is really easy to perform.

What went wrong in Windows 10 this week

This flaw pops up when users try to run a full scan — a quick scan won't have any issue completing. 

Under certain circumstances during a full scan, the Windows Defender Antivirus Service service crashes and leads to a tidal wave of error messages raining down from Event Viewer and Windows Security.

The crash, it turns out, is tied to files that have two consecutive dots in their file name, e,g, "thisisnuts..doc". It almost seems like a lamer version of the Y2K bug (ask your elders, kids). 

Windows Latest ties this issue to Windows Security Intelligence virus-definition update 1.313.1638.0, which it says was delivered earlier today.

While savvy users can go into Service Manager to put a stop to this, there's an easier way to fix things that brings us right back to where the problem began: a Windows update. 

Specifically, the fix is in Microsoft's latest antivirus and antispyware definition update, version 1.313.1687.0.

How to fix Windows Defender crashing bug in Windows 10

Yes, this issue that is apparently tied to something that happened in a previous update can be fixed by, you guessed it, downloading a new update. 

  1. Click the Start Menu button
  2. Type "Windows Security"
  3. Select Windows Security (App)
  4. Click Virus & threat protection.
  5. Under Virus & threat protection updates, click Check for updates.

Then, allow the updates to download and process, and enjoy Windows Defender once the update is applied and everything starts working right again.

This temporary calamity is a black eye on Windows Defender, which has been getting better and better as of late, has made it to the middle of our best free antivirus page and has given people a reason to think they might not need to pay for antivirus software anymore. 

It's also not the first bug to make things tough for Windows Defender, as last month we saw another issue that confused many people regarding files that the software was not scanning.

Henry T. Casey
Henry T. Casey

Henry was a managing editor at Tom’s Guide covering streaming media, laptops and all things Apple, reviewing devices and services for the past seven years. Prior to joining Tom's Guide, he reviewed software and hardware for TechRadar Pro, and interviewed artists for Patek Philippe International Magazine. He's also covered the wild world of professional wrestling for Cageside Seats, interviewing athletes and other industry veterans.