I think the source of these ads has been found. I had found a setting in avast! (a/v software) called Safe Price. It would display suggestions for a better price on things I was looking for at many stores. But I didn't care for the intrusions and its obvious tracking, so I unchecked that in the avast! settings.
Today, avast! was mentioned as a company that had started installing adware in its software without any fanfare. That led me to <
theSafeMac site> and Tom's free AppleScript, "Adware Removal Tool".
One of the adware 'app/code/extension' listed in the original article that started this trip, was MacVX. Turns out that is a Safari extension, I think it was called 'Pins' or something similar. At any rate, it's now in my Trash and soon to be picked up by the 'truck'!
So, if you've found some PopUps even though you have them "blocked" in Safari (and many other browsers) you might run the AppleScript and let it do a pretty fast search! BTW, if you don't want to run the script, Tom's site provides a very thorough list of adware and the tedious steps to take in searching the numerous directories on your system.
Hope this helps some one. No damage that I ever saw, which is why a/v software won't normally find/report these things; their not usually nefarious, so they are not technically "malware", just annoying! "Annoyware"?
Not a code "bug" but code that "bugs"!