How to fix latest file scanning flaw in Windows Defender May 2026

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How to fix latest file scanning flaw in Windows Defender May 2026

M L 10

Yesterday, 18 May 2026, I could use Defender to scan any downloaded file in my downloads folder by right clicking an item then selecting 'Show more options' from the drop down menu, then selecting 'Scan with Microsoft Defender' this would then trigger Microsoft Defender to scan the selected downloaded item and produce a Quick Scan report on the selected file. This is what Defender is supposed to be for, isn't it?, to detect bad items.

Today, when I select Defender to scan a selected downloaded file, it does..... NOTHING ! It does NOT trigger defender to action a Quick Scan on the selected item.

What happened overnight?

I am using the latest updated version 1.449.6920.0 which was automatically downloaded and installed from Defender itself this morning 19 May 2026.

I have tried a number of online fixes (none of them specific to this issue) from Microsoft and NONE OF THEM fixed this issue.

Is this issue a flaw/bug in the latest Defender update (above) or something else following May Patch Tuesday updates installation or the Windows Defender Exploits CVE in last few days? Microsoft has supposedly fixed the Blue Hammer flaw in Defender but there are apparently other flaw exploits stiill not fixed/patched.

Whats the score Microsoft Defender?

How do I/we fix this flaw ?

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Answer recommended by moderator

M L 10

So, no answers or suggestions from the community to this issue so I am left to carry on by single hand sorting out microsoft induced own operating system errors due to buggy updates that seem to cause glitches accross the windows 11 platform.

I fixed this issue myself since posting my help request by deleting the Windows Defender Operational logs in Event viewer.

Open Event Viewer, then expand > Applications and Services logs > Microsoft > Windows > Windows Defender > Operational. Select > Clear Logs in Actions, right pane. Select, Save or Don't Save. I selected Don't save, and so deleted the Operational log.

Windows Defender is now working as it should.

I hope, as human being to human being, this post helps you if you have the similar problem to mine.

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Answer 1

Thomas4-N 15,965 Microsoft External Staff Moderator

Hello M L,

Thanks for coming back to post what fixed it. The clear-log step will definitely give the next person hitting the same dead-end something concrete to try.

The reason it likely worked is that the Windows Defender Operational log is where Defender records every scan start, completion, and detection, and when that log gets into a bad state, the Quick Scan triggered by the right-click menu can fail to log its start and quietly do nothing, which matches exactly what you described. Clearing the log resets the channel, and Defender resumes writing to a clean one.

The recent Defender security news (BlueHammer, RedSun, and the May Patch Tuesday disclosures) is a separate topic. Those are privilege-related flaws that Microsoft patched through Windows Update, and none of them are documented to break the right-click scan menu.

I appreciate you taking the time to write the resolution up - This will be useful for the next person hitting the same silent no-op.

M L 10 Reputation points

2026-05-20T13:19:54.6333333+00:00

Hello Thomas4-N

Thank you so much for your very conversant reply.

Yes, I did make a point of posting the solution here because the remedy and cause due to WinDefender log jam is not well documented on line as far as I could see.

My issue appeared almost 'unique' as no other users were reporting exactly the same issue as mine.

I figured after reading along a very long way of looking for fixes about 'BlueHammer, et al, I wondered maybe this issue could be escalating, hence my post of the resolution.

Your answer has added to the collective understanding of what is actually going on under the bonnent/hood of Windows Defender, which in my view is probably the best protection and possibly why the creeps out there are trying to break it.

Lots of 'folk' like to bash Microsoft (I am not one) but I do get concerned when patch after patch seems to cause irritating glitches, like the one I describe.

Anyway, after I fixed my issue I noticed in my Reliabilty Report that WinDefender had downloaded and installed the following:

Update for Windows Security platform - KB5007651 (Version 10.0.29554.1001)

This (as you probably know, but i didn't) is an updated app version of Windows Security Center, otherwise known as Microsoft.SecHealthUI and get triggered when you run a particular PowerShell's Get-AppxPackage command.

Now, I do remember running various commands in PowerShell and none of them worked but it is possible I think that maybe I forgot to reboot one time after I possibly ran a command to reinstall the Windows SecHealthUI but didn't see if the result maybe also affected the solution of clearing the Defender logs/cache.

This is why I have asked Mahesh to populate his PowerShell commands and repost as I can maybe look back into my search history and find a match to the pwerShell command I used to trigger the update KB5007651, which incidentaly has a bit of old history to it.
Thomas4-N 15,965 Reputation points Microsoft External Staff Moderator

2026-05-21T13:24:00.0733333+00:00

Hello, thanks for the follow-up. It is helpful to have the additional detail around the Windows Security platform update and the possibility that more than one change (log clearing and the app refresh) may have contributed.

At this point it is difficult to isolate a single root cause after the fact, but having both observations documented here gives a clearer picture for anyone encountering a similar issue.
M L 10 Reputation points

2026-05-23T06:36:55.65+00:00

Hi Thomas4-N

Thanks for your reply. It was a tricky problem to solve and took a lot of time trying different fixes. No wonder I got a bit of brain fog after.

Just for clarity....

I remember now that after I did the log clearing I tried the app and it worked, which probably means log clearing was the solution because the app refresh I did using this PowerShell command:

Get-AppxPackage -AllUsers *Microsoft.Windows.SecHealthUI* | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

instigated when I rebooted the machine after the problem was already fixed.

It didn't hurt to do both but I think your are correct in your first Answer Reccomendation, as the log clearing option.

I think this report can now be closed as solved.

Thanks again for you helpfull comments.

Kind regards.

Answer 2

Hi Manesh

Just to be clear for you, before you posted, I ran all the options you itemise from 1 to 6 but none of them fixed the issue.

I also ran a full MSERT scan and a couple of Rootkit revealer tools and result were no infections, no rootkit and no apparent tampering with WinDefender. I was aware from years ago about the WinDefender Tampering pest but it is no present on my machine.

I was then pretty sure the issue was not an 'infection' but a glitch in my system - possibly caused by a update bug - hence I got into PowerShell commands but tried so many I lost track towards the end, hence my post asking you to repopulate your PowerShell commands particularly after from your Item 7, onwards.

Perhaps one of those PowerShell commands I did helped fix the issue but I forgot which one might have actually helped solve the issue - perhaps if we can pinpoint the commands we maybe able to help other users that might come accross this issue.

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How to fix latest file scanning flaw in Windows Defender May 2026

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