Yahoo! “tracking beacon”
Do you Yahoo!? Were you aware of this:
Yahoo is using something called “Web beacons” or a “super cookie” that tracks not only where its users go on the Yahoo network but also tracks where they go outside of the Yahoo network using a persistent file on the hard drive. Note that you have to have a Yahoo account to be tracked.
A9.com search will do the same thing if you’re signed in and using the A9 search engine (powered by Google).

