We perform a large-scale analysis of third-party trackers on the World Wide Web. We extract third-party embeddings from more than 3.5 billion web pages of the CommonCrawl 2012 corpus, and aggregate those to a dataset containing more than 140 million third-party embeddings in over 41 million domains. We study this data on several levels and provide the following contributions:
(1) Our work leverages the largest empirical web tracking dataset collected so far, and exceeds related studies by more than an order of magnitude in the number of domains and web pages analyzed. As our dataset also contains the link structure of the web, we are able to derive a ranking measure for tracker occurrences based on aggregated network centrality rather than simple domain counts. We make our extracted data and computed rankings available to the research community.
(2) On a global level, we give a precise figure for the extent of tracking, give insights into the structural properties of the ‘online tracking sphere’ and analyse which trackers (and subsequently, which companies) are used by how many websites, leveraging our ranking measure derived from the link structure of the web.
(3) On a country-specific level, we analyse which trackers are used by websites in different countries, and identify the countries in which websites choose significantly different trackers than in the rest of the world. In particular, the three tracking domains with the highest PageRank are all owned by Google. The only exception to this pattern are a handful of countries such as China and Russia. Our results suggest that this dominance is strongly associated with country-specific political factors such as freedom of the press.
(4) We investigate whether the content of websites influences the choice of trackers they use, leveraging more than ninety thousand categorized domains. In particular, we analyse whether highly privacy-critical websites about health and addiction make different choices of trackers than other websites. Our findings indicate that websites with highly privacy-critical content are less likely to contain trackers (60% vs 90% for other websites), even though the majority of them still do contain trackers.