some tracking methods do attempt to track the user over a long time, and in particular attempt to make it difficult to evade the tracking. This is sometimes done for advertisement purposes, but can also be done to stop certain attacks like brute forcing or to identify attackers that return to a site. In its worst case, from a private perspective, the tracking is done to follow a user across various web sites. Over the years, browsers and plugins have provided a number of ways to restrict this tracking. Here are some of the more common techniques how tracking is done and how the user can prevent (some of) it
» Johannes B. Ullrich | isc.sans.edu