Hello mdiRich!,
Malwarebytes isn't an anti-virus program. It is an adware/malware program. I have Malwarebytes many times on my computer to test it and have never had a problem with it. Malwarebytes and Etrecheck are two programs often recommended by long time posters.
It may be necessary to run more than one scan. After scanning a couple of times, restart the computer and test. If necessary, follow the manual instructions. Do not download any other programs that are listed in the articles. You have adware/malware.
See if the below helps the situation. I would scroll down to the below or you might fall asleep.
Step 1. Eliminate Yahoo Redirect from Windows.
Step 2. Delete Yahoo Redirect from Mac OS
Step 3. Uninstall Yahoo Redirect from Internet Explorer
Step 4. Remove Yahoo Redirect from Microsoft Edge.
Step 5. Erase Yahoo Redirect from Mozilla Firefox.
Step 6. Get rid of Yahoo Redirect from Google Chrome.
Step 7. Eliminate Yahoo Redirect from Safari.
https://www.2-spyware.com/remove-yahoo-redirect-virus.html.
Go to Safari Preferences/Extensions, uninstall any you don't recognize, and then turn all extensions off. Test. If okay, turn the extensions on one by one until you figure out what extension is causing the problem.
Safari/Preferences/General - see what the Home Page is set to. If something you don't recognize, see if you can replace it with something you want.
Safari menu/Clear History.
System Preferences and remove any Profiles you see.
Do not download any other programs that are listed in the articles.
Safe Finder Uninstall
Safe Finder Uninstall (2)
Safe Finder Uninstall (3)
{Information Above Given By Denis Root From Another Discussion}
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https://discussions.apple.com/thread/251414298
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King