Can you not exclude the entire Boinc directory?

I feel like a bit of an idiot because I should have thought of that. It worked. I excluded the entire directory and had to reboot. The problem went away after that.

Thanks for the help. (Now if I can just stop kicking myself...)

I spoke too soon. The problem has come back. This is only a recent issue. I wonder what changed (windows 10 update, new OP client, etc.)

Any more ideas? This is definitely associated with the anti-virus and the OP client.

You are not alone mwroggenbuck - I am seeing this too on a Windows 10 Home x64 version 20H2 machine of mine that is running OpenPandemics tasks. I actually first noticed this by observing a decline in points and results per day on one of my machines that started around March 11th/12th and then started taking a closer look. I have the 'C:\Program Files (x86)\BOINC' and 'C:\ProgramData\BOINC' directories on the excludes list in Windows Defender, but that doesn't seem to have any effect. I think it may be because the excludes list seems to be for actual scans and not for the real-time antimalware engine. After rebooting the computer and launching WCG, for 1-3 minutes everything looks OK but then the Antimalware Service Executable revs up and starts taking significant CPU resources.

I did review in my Windows Update history that the '2021-03 Cumulative Update for Windows 10 Version 20H2 for x64-based Systems (KB5000802)' was installed on 2021-03-10, which seems to match up with the timeline that both mwroggenbuck and I have observed on our Windows systems.

I'd be curious to hear if others are seeing similar behavior and if anyone has any other ideas besides completely turning Windows Defender off or switching to a different anti-malware provider.

Good idea Jorlin - I had not done that. Unfortunately, that didn't seem to do the trick. I added both the 'C:\Program Files (x86)\BOINC\boinc.exe' process and 'C:\Program Files (x86)\BOINC\boincmgr.exe' process (which I believe launches boinc.exe sometimes) to the Exclusions list and restarted the computer several times and I'm still seeing the significant CPU usage by the Antimalware Service Executable process.

Here is what my Windows Defender Exclusions settings look like: https://imgur.com/a/kT3uNp2

And here is what I'm seeing in task manager even after rebooting: https://imgur.com/a/9F8AXYR (Antimalware Service Executable being at the top of the list in Task Manager)

I've also confirmed this behavior is happening on more than one Windows 10 system - I've observed it thus far on a Windows 10 Education version 1909 system and a Windows 10 Home version 20H2. Both systems had installed the March OS patches from Microsoft and the issue seems to have started shortly after that. If I manually disable the real-time protection in the Windows Defender settings, that stops the Antimalware Service Executable from consuming significant CPU resources, but Windows eventually re-enables the real-time protection.

Any other thoughts/advice would be appreciated. Given that I'm seeing this on multiple systems and mwroggenbuck has seen it on at least one system, I'm guessing quite a few people with Windows 10 systems could be impacted without necessarily knowing it. For me, the only reason I caught it is that I noticed my PPD and results/day were down ~8-12% which then caused me to investigate and then come to the forums to see if others were seeing anything similar.