Internet users who are actively trying to make sure their online activity isn’t tracked by websites or government agencies should know there’s an even creepier tracking tool out there used by a variety of websites, “from WhiteHouse.gov to YouPorn,” as ProPublica puts it, that’s almost impossible to block.

Called “canvas fingerprinting,” the tool built by AddThis instructs web browsers to create a hidden, unique image that can be used to track the user’s movements from site to site – much like a fingerprint – in order to deliver better targeted ads. The technology began testing earlier this year as a way to replace website cookies.

Canvas fingerprinting has been first observed by researchers at Princeton University and KU Leuven University in Belgium, who wrote a paper on it, and it’s apparently very difficult to block.

The online tools that prevent online tracking can’t fight this particular type of technology, so don’t go to AdBlock Plus hoping that your problems will be solved. Incognito modes available on browsers are also not able to protect the user’s privacy by avoiding canvas fingerprinting, which means that parties using the technology will still be able to track users who think they’re safe behind incognito browser features.

There’s currently no tool that will offer a hassle-free way of blocking canvas fingerprinting, but Gizmodo offers various ways of trying to fight it. Users can either use Tor, install a NoScript Firefox extension, download and use the Chameleon browser or blocking JavaScript from a browser altogether, but either choice may also offer a worse Internet browsing experience.

AddThis told ProPublica that so far it has used the data obtained from its technology only from internal research and development, and that an AddThis opt-out cookie exists, and can be installed in order to stop AddThis from using data for ad targeting and personalization.

The company has apparently rolled out the feature to a “small portion of the 13 million websites on which its technology appears,” without notifying websites about it. The company also said the technique is not “uniquely identifying enough,” adding that it won’t use tracking data from governmental sites for ad purposes.

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In a follow-up comment, a YouPorn representative said the company was not aware of the tracking feature, and that AddThis technology has now been removed upon discovery of the canvas fingerprinting tracking feature.

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