Abstract
Websites are constantly adapting the methods used, and intensity with which they track online visitors. However, the wide-range enforcements of regulations such us GDPR and e-Privacy has forced websites serving EU-based online visitors to eliminate, or at least reduce, such tracking activity, given they receive proper user consent. Thus, it is important to analyze the aftermath of such policies, record the evolution of this tracking activity, and assess the overall " privacy health " of the Web ecosystem. This work makes a significant step towards this direction. In this paper, we analyze the ecosystem of 3rd-parties embedded in top websites, which amass the majority of online tracking, through six time snapshots taken every few months apart, in the duration of the last few years. We perform this analysis in three ways: 1) by looking into the network activity that 3rd-parties impose on each publisher hosting them, 2) by constructing a bipartite graph of " publisher-to-tracker " , connecting 3rd-parties with their publishers, 3) by constructing a " tracker-to-tracker " graph connecting 3rd-parties who are commonly found in publishers. We record significant changes through time in number of trackers, traffic induced in publishers, embeddedness of trackers in publishers, popularity and mixture of trackers across publishers. In the last level of analysis, we dig deeper and look into the interconnectivity of trackers, and how this relates to potential cookie synchronization activity.