Very recently and only on Chowhound I'm getting disruptive full-page pop-up ads for "Opinion Central," the market research firm. I know how to get rid of them but unlike normal Chowhound advertising, they wipe out the whole screen, interrupt whatever the user is trying to see, and are disruptive overall, discouraging use of Chowhound. (The ads replace a newly loaded page with a huge "want to take a survey?" button.) They aren't carried over from some other site because the computer is wiped clean after each use.
Maybe they come indirectly through one of the other advertisers, but I wonder if CH is aware of this and of how offensive it is.