It is almost impossible for computer users to detect new, legal techniques employed by major Web sites that track people's online activities through the installation of files called supercookies.
Researchers at Stanford University and the University of California, Berkeley say that supercookies can re-create users' profiles after they have erased regular cookies. Supercookies are stored in different places than regular cookies, such as inside the Web browser's cache of previously visited Web sites.
The Berkeley researchers determined, for example, that Hulu.com was using supercookie methods to store tracking coding in files related to Adobe Systems' Flash player, which enables numerous online videos. They also discovered that Hulu's Web site featured code from Kissmetrics, a firm that analyzes Web site traffic data, and which was embedding supercookies within users' browser caches and into files associated with the latest iteration of HTML.
Meanwhile, a Stanford researcher has identified a history-stealing tracking service on Flixster.com, which uses software to mine a person's Web browser history on their computer to try to ascertain the sites the person has visited. The company then uses that information for targeted advertising.
From Wall Street Journal
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