Virus Notification

Get rid of the source of the notification. In the Safari setting go to Websites > Notifications and delete the website sending the notification. These are scams that will lead you to a variety of sites including ones that say your iCloud storage is infected. It will then collect any data you have synced to iCloud.

Scan you Mac for malware as well as the hacker who got into you system will have access until you get rid of any malware and have a malware/antivirus app installed and running.

If this is showing as a Notification from the top corner, please refer to the user tip below.

Stop unwanted Notifications - Apple Community

You are quite welcome, and thanks for the feedback.