How to stop unwanted Spam Pop-ups on MacBook?

I'd like to start with this: I do not have the McAfee virus protection software, period. I have a new MacBook Pro, and have been just scanning once in awhile with the free version of Malwarebytes. the McAfee pop-ups looked suspicious so I didn't click, but instead ran a scan by Malwarebytes - it did not detect anything. They are tricky little pop-ups, too. I tried to screen capture them and they disappear before I can do that. Given this information, would someone please reply about whether I still need to contact McAfee even though I don't have their software?

[Re-Titled By Moderator]