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A research conducted by Mozilla found that browsing histories are unique enough to identify users reliably, breaking the myth that anonymised browsing history isn’t useful to online advertisers.
Researchers looked at the privacy provided by browsing histories and concluded that even a small list of 50 to 150 of user’s most accessed websites are enough for advertisers to create a unique tracking profile.
This could be used to identify users across any set of data that contain even small samples of the browsing history. The study said that that general audiences are not aware that privacy protection tools exist, let alone understand their function or the threats they protect against.
The Mozilla research paper titled Replication: Why We Still Can't Browse in Peace: On the Uniqueness and Reidentifiability of Web Browsing Histories was presented in August at the USENIX security conference.
Mozilla conducted a similar study in 2012 to analyse user privacy. It collected browsing history data of 380,000 internet users. Following up on that research, Mozilla decided to re-examine the study and see if that still holds true.
Between July 16 and August 13 last year Mozilla requested its users to take part in an anonymous browsing data survey. As a result, it collected data of 52,000 users in two stages over two-week period to see whether they could re-identify users.
The final dataset ultimately contained about 35 million website visits and 660,000 distinct domains. Mozilla said that 99% of the profiles they collected were unique to each user. High uniqueness held even when histories were truncated to just 100 top sites.
Users who visited 50 or more distinct domains in the two-week data collection period, almost 50% can be re-identified using the top 10k sites. Re-identifiability rose to over 80% for users that browsed 150 or more distinct domains.
“We observe numerous third parties pervasive enough to gather web histories sufficient to leverage browsing history as an identifier,” Mozilla said.
This suggests that online advertisers don’t require a large set of browsing data to track users, only a user’s browsing quirks and favourite sites are enough to help them create unique profiles.
