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I have a Windows Server 2019 virtual machine hosted on Azure. For the last two or three days, web applications hosted there have been very slow.

Yesterday I started digging into it, and found that Windows Defender (MsMpEng.exe, and MsSense.exe to a lower extent) have been using close to 100% of CPU:

Task Manager

I have been googling and found a lot of articles describing this behaviour for Windows 10, with multiple solutions.

I have tried adding the Windows Defender folder to the exclusion list to no avail. The server is fully updated, and I have restarted it several times.

I looked at the Task Scheduler solution (modifying the Scheduled Scan) and I changed it to weekly, although Windows Defender reports it's a quick scan that only takes 3 minutes:

Windows Defender Quick Scan

I just noticed that the last successful scan was on 4/27. I just changed the scheduled task frequency today, so we are missing the 4/28 and 4/29 3:00 am scans. So I guess the issue started at some point on 4/27 after 3 am.

These are the updates installed since that time:

Windows Update history

I am trying to install those updates as I write this (you know, slow system...)

Has anyone of you seen a similar symptom? Any ideas?

Thanks,

Luis

Luis Alonso Ramos
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  • Windows won't let me uninstall Windows Defender definitions, just actual software updates. – Luis Alonso Ramos Apr 29 '23 at 17:35
  • I could rollback the latest definition update according to this page, but running it a second time would not roll back the second to last update. All I could do was go back to 2599. https://www.microsoft.com/en-us/wdsi/defenderupdates – Luis Alonso Ramos Apr 29 '23 at 18:28

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