I've been seeing large, near full page pop-ups that pretend to be browser warnings. These do not appear to be Adsense.
On desktop sites I've seen pop-ups saying "Microsoft has detected... Follow instructions to fix... and remove the virus from your computer." This link leads to page selling scan software with a large Download button.
On mobile I've seen a similar overlay ad using Google's multicolor logo. The message even sniffs my OS and identifys my phone make & model.
Just more damage done to the internet experience