Windows Antimalware extreme SSD usage - Solved

[iamgigglz]

After installing Windows on my PC I've noticed that "Antimalware Service Exectuable" is just going ham on my SSD, using 500MB/s for hours on end, stops for maybe an hour or two, then kicks off again.
500MB/s isn't saturating my nvme SSD but it's enough to drastically lower performance on anything else that uses the drive.

Googling it suggested changing the Task Scheduler entry for Windows Defender, and adding the scan service as an exception, neither of which has had any effect.
I understand that occasional full scans are necessary but this seems broken.

Any other ideas?

 

[ED209]

Have you made sure all Windows updates are installed? Could be fixed in an update and not installed if its a clean install.

 

[iamgigglz]

Have you made sure all Windows updates are installed? Could be fixed in an update and not installed if its a clean install.

I usually check for updates after a fresh install - I see now there's KB5089573 which is a big deal performance-wise. Let's see if that helps.

 

[mattyfez]

Check windows update again afterwards so make sure there's nothing outstanding, as it's possible some updates are dependent on previous updates being present

 

[iamgigglz]

Ok, mystery solved. It was the Linux ISOs I was downloading which contain zip archives. I think that as the download progressed the zip file's size/fingerprint kept changing, which triggered a Defender scan of the contents again and again and again.