Simon Willison’s Weblog

evercookie - virtually irrevocable persistent cookies (via) Mischievous genius from the chap who created the MySpace worm—evercookie attempts to set an irrevocable cookie using a whole bunch of different methods, including “storing cookies in RGB values of auto-generated, force-cached PNGs using HTML5 Canvas tag to read pixels back out” and an extremely clever scheme built on top of the web history CSS visited link colour vulnerability.