Windows 10: High CPU usage from Windows Defender

I have W10 Pro, version 1803, build 17134.19 (although these issues started when I was still on whatever the previous build was numbered) with a i7-6700k, 16gb RAM and a Samsung 750 EVO 500gb.

As of the past week or so I've noticed that Windows Defender's CPU usage, specifically from MsMpEng.exe (Antimalware Service Executable), has increased dramatically when opening/closing certain programs, namely Windows Update in Settings and Firefox.

Whenever I open up "Update & Security" in the Settings app or start/exit Firefox, it not only causes MsMpEng's CPU usage to spike up to 10-15% for the next 20 or so seconds, but also slow down other programs running on my computer during that time. Nothing else has ever slowed down my computer like this, not even games running on max settings - which I should add, typically use MORE than 10-15% CPU.

While it's entirely possible that Defender has always spiked to 10-15% CPU usage considering I've never really had a reason to pay attention to it before, it's never caused the slowdown until recently.

I can circumvent the CPU spikes for Firefox by adding the Firefox process/folders to Defender exclusions, but I haven't found out what to exclude for Windows Settings/Update other than the entire C:\Windows folder, which does work but seems rather excessive.

I've already tried running a full malware scan (came back clean) and sfc/ scannow (also came back clean). Nothing else on my computer has been having issues, just this.

So has anyone else been having increased CPU usage from Defender as of late, or am I the only one? Could a problematic Defender update have caused this?

According to Google I'm not the only one who has encountered the Firefox-Defender CPU usage issue recently but I haven't been able to find anything about any Windows Update-Defender CPU usage issues.

:)

 

VERY HIGH CPU USAGE

Hey there Kristian, first I'd suggest using your task manager and seeing if Windows antimalware executable is going on, because it can spike high cpu usage rates. Afterwords, i'd like for you to do a scan with your windows defender, as it may be malware
infecting your computer.

 

Defender showing high cpu usage

Why is Windows Defender showing high CPU usage >40% when i am not running a scan. I ran a full scan yesterday which almost ran for 4 hrs and yet didn't complete. So I cancelled the scan and today i am seeing CPU usage of upto 50% by the Anti-malware service
executable process.

 

high cpu usage

After downloading windows 10, anytime I run any programs, I get high CPU usage. It does not matter whether it is google chrome, task manager, playing games, whatever. Anything seems to spike the CPU usage. I have already run malwarbytes and my antivirus
programs and find no viruses. Any suggestions? Thanks.