Virus alert

Those are website notifications. The reason for their appearance is that agreed to have one or more websites send them.

Stop them by following these instructions:

• Go to Safari's Settings (or Preferences) menu > Websites > Notifications, and remove everything there.

For reference: Change Websites settings in Safari on Mac - Apple Support

Don't allow websites to send you Notifications unless you are 100% certain you want them. I cannot think of a single reason anyone would want to invite that kind of harassment.

Refer to Customize website notifications in Safari on Mac - Apple Support. Deselecting "Allow websites to ask for permission to send notifications" will prevent those websites from even asking your permission to be harassed by them.

I am getting these popups every few seconds nonstop. I was concerned because even though I know they are scams, they appear to be official messages coming through the system settings. I get about twenty different messages. I tried your solution but each time I choose to Deny System Alert, everything freezes up. I have to force quit Safari and try again but the same thing happens. For reference, I have never subscribed to either McAfee or Norton despite the messages that my subscription expired. I do use Malwarebytes which was recommended by Apple and it shows no sign of any problem.

I had been attempting to Deny the notifications and the browser kept freezing. This time I removed them following John's diagram below. Hopefully the problem will now be solved. It had just started a few days ago out of nowhere and was driving me nuts.

These complaints became so common I distilled everthing into the following User Tip:

Stop unwanted Notifications - Apple Community

It's a scam; ignore it. You likely picked this up from a website you visited or the current website you're on.

Please read through the advice posted by John Galt above, especially the part regarding Safari Settings.