An in-depth exploration of a new method used by tracking companies to disguise their third-party trackers as first-party trackers.

Criteo built itself into one of the star performers in the ad tech sector by using a technique called “retargeting”--serving ads to people who have already visited a website to remind them to return.

Retargeting relies heavily on dropping cookies to track users as they leave one website and continue browsing elsewhere on the web.