I getting these too, says I've won a free Iphone. Pops up at the most inconvenient times.
I can't seem to identify when it pops up. Maybe it is related to Facebook, but not sure.
It's too bad there is no real advice on what to do anywhere.
All's folks can offer here is "run a scan".
I do have the Malware Bytes app, but it will not complete it's scan without crashing, so far.
THAT'S not good.
I'm going to download the BitDefender app and see if that helps.
Does seems like maybe my browser has been highjacked but I don't need to be using the browser for the pop up to appear.
Can't seem to find much detailed advice.