Systems such as DoubleClick can identify up to 90% of users.

Back in December last year, documents appeared that revealed some features of the work of specialists from the ill-fated NSA agency. It turned out that the employees of this agency could, without any problems, track web users using DoubleClick cookies.

Now there is a publication from the Princeton team of experts, which claims that NSA capabilities are not even needed to track users. For example, the Princeton team of experts was able to identify up to 90% of users by monitoring the traffic of systems like Google’s DoubleClick.
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No special data access is required. Experts simply monitor open network traffic.

As it turned out, such systems allow you to get a lot of information about their users. In particular, each advertising system provides a unique user ID, but the researchers were able to track the web requests of specific users, grouping data using the same browser session from system to system.

Using the same cookies on social networks, researchers were able to identify users whose requests were already tracked. As mentioned above, this method allows you to identify about 90% of users, which is very good.

Result: for each specific page view (pageview), you can define the user and the pages that this user has viewed. Security measures such as the https protocol made the user requests a bit more complicated, but the number of advertising cookies made the identification of users quite simple.

As far as can be understood, only protection using Tor networks makes it impossible to track a user on the network.

Via theverge