ShareThis and AddThis are now including a “canvas fingerprint” for each user who visits the assoicated site. Canvas Fingerprinting uses new drawing technologies in HTML5 to uniquely identify a user’s browser without using the more standard web technology – cookies. At first, this doesn’t seem to be an issue, after all Sitecore’s DMS provides a first-party cookie used for Analytics and Google Analytics does the same with a 3rd party cookie.
What gives me pause is that ShareThis and AddThis are not doing this for the benefit of the user experience on our website with data retained there, but instead are capturing the traffic of a user across multiple websites so that more information can be gathered for the purposes of advertising.
Is this a big deal? Perhaps not. The web is full of tracking, even across sites. When I view an item on Amazon, that item is later advertised to me on my favorite news websites through re-targeting advertising. However, tools like ShareThis and AddThis provide functionality that is easily replaced with custom logic that does not expose our users to one extra level of tracking.