Norton and McAfee virus infection
My 13in MacBook Air has become infected with both Norton and McAfee antivirus adverts. What to do?
MacBook Air 13″, macOS 10.13
If you are seeing them in the upper right of your screen as a Notification, then go to Safari > Settings > Websites > Notifications, and remove all sites that you have allowed to send you these Notifications.
These will appear to look like the ones in this support article about unwanted notification.