An extremely persistent type of online tracking is shadowing visitors to thousands of top websites.
Called canvas fingerprinting, it works by instructing the visitor’s web browser to draw a hidden image and they can be used to assign each user’s device a number that uniquely identifies it. They are unusually hard to block and cannot be prevented by using standard Web browser privacy settings or using anti-tracking tools such as AdBlock Plus.
According to researchers, canvas fingerprinting computer code is primarily written by a company called AddThis, on five per cent of the top 100,000 websites and most of the code was on websites which uses AddThis’ social media sharing tools. AddThis’ chief executive said that the company began testing canvas fingerprinting earlier this year as a possible way to replace “cookies,” the traditional way that users are tracked, via text files installed on their computers.
