Reviving this, as I wanted to check my notes before commenting, and I just found them:
DD recently told me she was having problems with her MacBook Pro, her browsers had underlines for all the text which linked to ads, and ads would pop up and open new windows, and take over her home page. Not good.
She said it seemed to happen after she downloaded some Adobe software she needed for a school project - but.... she didn't remember where she downloaded it from. So I suspect that was a scam site, and told her always go directly to the source (Adobe in this case), and download it from their site.
So some googling, and I find references to "Trovi adware".
How to remove Trovi adware from Mac
It basically involved resetting the browser and doing a bunch of searches to find and remove files with some of the names they list. Fixed it.