Are you sure that just disabling real-time protection allows for deleting those files? I'd be surprised if it did, I think you need to actually disable Defender altogether to be allowed to delete.
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At least for me I can confirm without any doubt that my issues has been resolved by the steps outlined in this thread. It is of course possible that Avast Free steals less resources overall, but I'm...

Interesting. In my case the system was actually slowed down even when Defender was not using a lot of CPU.

My best guess is that issues with the db file can manifest itself as different symptoms....

ignatzatsonic: If disabling real-time protection in Defender solves the problem, then I am unsure if it is actually the same problem. In my testing, I saw no improvement from disabling the real-time...

You are not going to delete msmpeng.exe! The key file to delete is mpenginedb.db, as outlined above.

As I mentioned, I didn't really think that my issue with this was solved, even if that periodic CPU usage went away after manipulating the scheduled tasks. No matter what, the computer was clearly...

It seems there are multiple problems here, but I can also confirm that it can help to add the process (not the file or path, but the process) "firefox.exe" to exclusions in Windows Defender. It's not...

It sure seems that this is a more widespread issue than what I thought, but it clearly does not affect everyone, or else the outcry would have been even bigger.

Now, I have something more to...

I've done that now (right-clicked on all four tasks/schedules in Task Scheduler) and disabled them, like so:

198470

That's what you meant, right? I'll report back later.

Another piece of information: It seems it isn't as random as I thought, at least not today. It seems to run in cycles, starting the CPU usage around every 16 minutes, running for approximately 4...

Adding that folder exclusion did nothing, as suspected. This all seems rather random, and it would have been nice to be able to find out what Defender is doing with those CPU cycles, because it sure...

Yes, it may well be that there is a bug in the current Defender, but probably only some people are affected.

I will try to add an exclusion for the folder mentioned, but I already have an...

ignatzatsonic: I am also seeing that file being accessed by the process (not sure it is scanning it, though), but it does not correlate with the elevated CPU usage. This file is more or less accessed...

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...