I've had this same problem for ~18 months right after I downloaded Adobe Flash Player (a recent version 18 months ago) and I've deleted the obvious files, multiple times. It could be a coincidence if the code related to the ad was downloaded unbeknownst to me, via another update, etc. Non of the download/update dates matched. I uninstalled Adobe Flash Player maybe six months ago, then downloaded the most recent free version directly from Adobe. Within a couple weeks the pop up ads were back. I deleted any obvious files again several times, but a different looking ad just popped up today and is similar to previous versions of the pop up, so I knew what it was. And I can't find the files anywhere to delete them.
Another contributor mentioned downloading something Adobe-related. Maybe that's the root?
Tomorrow after a back up, I will let you know which of the suggestions in this string still work as of today.