Unwitting AddThis Experiment With Tracking Technology That Is Difficult To Block

https://www.techdirt.com/articles/20140721/14523127960/tons-sites-including-whitehousegov-ex...
ProPublica has a new story about the rise of "canvas fingerprinting," a new method of tracking users without using cookies. It's a method that is apparently quite difficult to block if you're using anything other than Tor Browser. In short, canvas fingerprinting works by sending some instructions to your browser to draw a hidden image -- but does so in a manner making use of some of the unique features of your computer, such that each resulting image is likely to be unique (or nearly unique). The key issue here is that the popular "social sharing" company AddThis, which many sites (note: not ours) use to add "social" buttons to their website, had been experimenting with canvas fingerprinting to identify users even if they don't use cookies. As ProPublica's Julia Angwin notes, it's very difficult to block this kind of thing -- and tons of sites make use of AddThis -- including WhiteHouse.gov (whose privacy policy does not seem to reveal this, saying it only uses Google Analytics as a third party provider).

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