Once on a search reslutls page, there was a banner ad served by doubleclick on the top of the page. I was studying the page for a long time, and all of a sudden, I thought the ad changed to a different ad.

A few days later, I was downloading a new song and video on shockwave.com (it's called "I Hate My ISP" by Todd Rundgren) Half way through the 8 minute download, I could swear the doubleclick ad changed again.

Is there such a technology? Can doubleclick serve more than one ad to the same page and just push it to you, even though you only asked for one page view?