Researchers reveal that Google-owned domains, from where browsers load tracking code, account for the top 5 most popular trackers and 12 of the top 20 tracker domains.
In fact, after studying the Top 1 Million sites, researchers discovered over 81,000 different domains from where tracking code was loaded. Taking a closer look at the data researchers said that only 123 of these third-party trackers are found on more than 1 percent of all sites.
"This suggests that the number of third parties that a regular user will encounter on a daily basis is relatively small," Princeton Web Census researchers explained. "The effect is accentuated when we consider that different third parties may be owned by the same entity. In fact, Google, Facebook, and Twitter are the only third-party entities present on more than 10% of sites."
All of this means there's a high chance that you visit a website, or click on a link, and that one of the three companies mentioned above already knows about it. This is certainly true for Google, who loads some sort of tracking code on four out of five websites.