A gray message with a setting wheel (trying to look like an Apple settings gear) pops up in the top right corner of my Mac screen. It varies from Norton ads, antivirus ads, msgs my computer is corrupt or has 5 viruses, etc. How do I stop it?

A site you visited has given itself permission to send push notifications. Everything you're seeing is nothing but a scam.

Open Safari's preferences. Click on the Websites tab and then scroll down to Notifications. Clear any entries in the right hand window. You might find something similar in the Pop-up Windows heading below that. Block any you don't recognize.

Then if you want, uncheck the box below as shown here.

I personally can't think of any reason why I would ever want any website to push notices to me.

You're welcome. 🙂