High CPU usage from Windows Defender

I just manually scanned the USOShared folder with Defender, finished in less than a second without any slowdown. I suppose the slowdown only happens when Defender decides to scan the folder and its files while the files are being rewritten at the same time.

For what it's worth I also tried a full system scan with Defender while paying attention to its CPU usage. While it does use up 10%-20% CPU while scanning, nothing else gets slowed down at the same time. Hell, Malwarebytes typically uses 50%+ CPU while scanning and that never simultaneously slowed down anything.

I have found out that you can actually flush ProgramData\USOShared folder contents. They seem to be just logs.

I'm having this same issue, Windows taking abnormally long to load general tasks like web browsing and Task Manager, only clue is the Antimalware Service Executable using 15% CPU. It's not consistent either. So far the fixes I've seen like adding exclusions to Defender have not solved it. The performance monitor shows the service scanning pretty much everything I do, which I believe is what it is supposed to do...?

I think it *might* have something to do with Task Scheduler. I'm wondering if making the Conditions for the the Defender Scheduled Scan more strict might get it to chill out.

Yup, looks just like the picture on the page most of the time with the NTFS volume log and mpengine. Aside from the Defender files it looks as though it's scanning everything I touch, most browser cache files. I actually tried clearing all temp files and browser caches but it didn't seem to help.

Why On my Systems I just stick with Avast Free, which eliminates the high cpu usage from Defender, despite I kinda like Defender for it's no ads, silent protection it gives, May have to just deal with ads and just use Avast on the systems, and be happy systems are free from any sort of infection

Yup, just disk activity. I've been seeing articles like those and am not sure any of those fixes actually work as most just involve disabling Defender. They're also inconsistent, some say to add Program Data\Windows Defender and some say Program Files\Windows Defender. I suppose I could try adding both.

Here's how the Resource Monitor looks on mine when it occurs.

I have the same issue, and it is driving me crazy. I'm still on 1709, so it's nothing to do with 1803.

In my case, I have a feeling it appeared after I updated my BIOS (Asus Sabertooth Z170 mark 1) to version 3801. I mainly did that because I had unexplained reboots (which I've also had in the past), but it also brought in protection against Spectre.

What happens is that the Antimalware process seems to kick in rather randomly, and it always consumes just around 12-13% CPU. Sometimes it sits there for a few minutes, other times it just cycles usage in periods of around 12 seconds (but when it is "on", it is still those same 12-13% CPU).

The funny thing is that using resource monitor, it does not seem to do anything except consume CPU. Under disk activity there is nothing extraordinary, it doesn't seem to do any actual scanning. And that's the real bugger, what the heck is it using those CPU cycles for? It makes the computer rather sluggish, and opening programs while this is going on takes quite a bit of time (a good few seconds to open task manager (Ctrl-Shift-Esc) for instance, which usually just pops up instantly). More time than what you'd assume from the load (after all, 12-13% isn't that high).

I've tried all of the suggested solutions, and the only one that actually works is to disable it altogether. I know many people would recommend that, but up until now I've been satisfied with it, so no reason to install some other AV solution.

So how on earth can I find out what the Antimalware process is using those CPU cycles for?

I'm running a Skylake i6700k (at stock speed) with 32 GB of RAM, BTW.