  Websites are constantly adapting the methods used, and intensity with which
they track online visitors. However, the wide-range enforcement of GDPR since
one year ago (May 2018) forced websites serving EU-based online visitors to
eliminate or at least reduce such tracking activity, given they receive proper
user consent. Therefore, it is important to record and analyze the evolution of
this tracking activity and assess the overall "privacy health" of the Web
ecosystem and if it is better after GDPR enforcement. This work makes a
significant step towards this direction. In this paper, we analyze the online
ecosystem of 3rd-parties embedded in top websites which amass the majority of
online tracking through 6 time snapshots taken every few months apart, in the
duration of the last 2 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 (incoming vs. outgoing), embeddedness of trackers
in publishers, popularity and mixture of trackers across publishers. We also
report how such measures compare with the ranking of publishers based on Alexa.
On the last level of our analysis, we dig deeper and look into the connectivity
of trackers with each other and how this relates to potential cookie
synchronization activity.
