· About 3 minutes read

Tracking without cookies

During a session at IDP 2011 (conference on Internet, Law and Politics) in Barcelona I started thinking about the issue of opt-outs / opt-ins for tracking cookies. If we were to imagine a situation where most people reject tracking cookies – which would be nice – then those who are interested in tracking users would have to resort to other methods.

I just came up with one.

I haven’t seen this before but it’s fairly obvious, I’m sure that there are dozens of variations on this theme or even much better approaches. By “better” I mean “more effective”, not necessarily nicer – violating people’s privacy is not nice.

First, create a hidden

containing a bunch of links, to, for example, http://smarimccarthy.com/tracking/X, with X equals numbers from 1 to 33. 33 is enough because 2^33 is greater than the number of humans (by about a billion), but you might want to add more links. The
is hidden using the display:none CSS directive.

When the page is loaded a Javascript on the page checks each of them in sequence to see if they’ve been “clicked”, by reading the “visited” property. If none of them have been clicked, send request to server (over AJAX) which sends back a number (between 1 and 2^33). That number is decomposed and certain links opened in hidden