Arvind Narayanan writes:
A frequent misconception of Do Not Track is that the goal is to prevent tracking by online advertisers. In fact, tracking is a much broader problem on the web, and our Do Not Track vision at Stanford, while principally aimed at “third-party” tracking, does not focus on specific industry segments.
[…]
What are some examples of third-party tracking not directly related to behavioral advertising? The Facebook “like” button is a prominent one — Facebook can keep track of all the pages you visit that incorporate the button, whether or not you click it. Did you know, for example, that the UK National Health Services website has the like button, among other trackers, on all their disease pages?
Read more on The Center for Internet and Society (Stanford Law School)