Saw this posted on Anandtech Forums by alm4rr, who quoted its source, located here:
http://www.lurhq.com/iframeads.htm
"Virtumonde is a well-known adware trojan that hijacks victim browsers and forces them to display popup ads based on keywords in the sites they are visiting. For instance, a user visiting a page with keywords related to travel may display popup ads for sites such as vipfares.com, a discount-travel site with a long list of customer complaints about fraudulent practices."
See the site for more info and a list of known URLs that have the trojan.