A recent study launched by the UC San Diego Department of Computer Science to determine the scope of privacy-violating information flows at popular websites shows that Web 2.0 applications such as mashups, aggregators, and sophisticated ad targeting are teeming with various kinds of private information flows. The researchers determined that such attacks are not being adequately defended against. The goal was to draw attention to the prevalence of history sniffing at high traffic sites. Sites use these exploits to gather browsing information about patrons and then use the information to target ads and determine whether patrons are visiting competing sites.
Source: https://threatpost.com/study-finds-popular-sites-guilty-hi-jacking-history-120610/74729/