Stopping MRT

For the most part MalwareBytes is not really needed. MRT or Malware Removal Tool is part of the built-in anti-malware software of macOS. That said, there should be a reason why MRT is spiking CPU usage given that it is a background process. You might consider removing MalwareBytes temporarily to see if that has any effect on MRT. You can also try running the computer in Safe Mode to see if that affects MRT's spiking usage.

About Using Safe Mode

• Use safe mode to isolate issues with your Mac - Apple Support
• Playing Safe- what does Safe mode do?

Boot Into Safe Mode

1. If your Mac isn’t already shut down, then shut it down and wait at least 30 seconds before rebooting.
2. Immediately, at or before the chime, press and hold down the SHIFT key. 
3. Release the key after the Apple logo and progress bar appear.
4. Safe mode startup is much slower than normal startup, so be patient.
5. When the Login Screen appears enter your admin password. If you use automatic login, then this means you are in safe mode.

MRT is the built-in Malware Removal Tool. You don't want to remove it nor any of the files it creates. The ones you listed are needed parts of the MRT package. They are kept in Receipts because they used to keep track of upgrades to MRT.

Please do not remove any of these files or your computer will become completely open to security risks from malicious malware. I realize it appears that the tool sometimes uses a lot of CPU time but sometimes this may be normal (I don't have any idea about what normal is for the MRT.) I sometimes see all the cores on my iMac using a lot of processing time when Spotlight is indexing.

Now, that said it's possible for some files to become corrupted, thus, causing serious problems for the CPU. The most frequent culprit is caches that become corrupted. There are Caches folders in all the Library folders use by macOS. Most can be removed (but not all) because they will rebuild automatically when called for. One way to get some essential caches remove and rebuilt is to boot the computer into Safe Mode, then reboot normally. This clears some caches.

Another group of files that get corrupted is preference (usually, .plist files) files.

If you do a Google search using "what is mrt in macOS" for the search term, then you will find lots of informative material about MRT.

Thank you for your response. I ran in Safe Mode for a couple of days - MRT did not go haywire in that time. But the 100% CPU looping did recur 15 days later.

Does anyone know if these files created by MRT are important? They are paired, and created once or twice a month. Some months are skipped. I can't imagine three-year old files are useful.

In any event you can't send them to Trash.

Maybe the question is can I be rid of MRT altogether?? It lives in /Library/CoreServices which seems "important". I certainly don't want to break my dear iMac.

Thanks for your helpful response. I would now assume MRT is really doing something when it runs both cores at 100%. I'll let it run next time to see if it completes. I can still get work done in this state. Bottom line for me is "let it be".