The research has been commissioned by the Belgian data protection agency, which is investigating Facebook. It was a collaboration between the Interdisciplinary Centre for Law and ICT/Centre for Intellectual Property Rights (ICRI/CIR) at the University of Leuven and the Department of Studies on Media, Information, and Telecommunication (SMIT) of the Vrije Universiteit Brussels.
This newly found tracking, used to provide targeted advertising, is carried out through Facebook’s social widget, the Like Button. A cookie is placed in the browser when someone visits any page in the facebook.com domain, including sections that do not require an account. For visitors that are not Facebook users, the cookie contains a unique identifier, and it has an expiration date of two years. Facebook users receive additional cookies that identify them uniquely. Once those cookies have been set, Facebook will receive them for every subsequent visit to a website that uses Facebook’s social widget. That applies whether or not the Facebook user is logged in to his or her account and whether or not the visitor to the third-party site actually uses the social widget.