Safari redirects to Yahoo every time.

IMac running High Sierra.

I've looked up everything on the support forum and tried it.

I've tried Malwarebytes, but it doesnt work.

It detects and quarantines the malware, but it pops up again 2 minutes later.

I've checked and deleted the only profile that was there.

There are no extensions in the Safari Preferences.

Safari is set to start and search on Google.

I've cleared out Launchagents and app support folders etc etc..

Updated the Mac with the latest security update.

But nothing has managed to get rid of this.

No

I've run out of things to try.

Any ideas?