I am getting a pop-up 'message' several times a day from a malware malicioous virus. How can I just block it out permanently?us site. Norton blocks it fine. But how c

I first received a -up  pop'message' from McAffee that my computer was infected with multiple viruses and I needed to subscribe to them to get it fixed.  I do not now nor have I ever had a subscription to McAfee.  Norton blocks these each time..or I sometimes can just X it closed...but how I just put a stop to it all?