Privacy analysis of FLoC (Mozilla blog)

Over on the Mozilla blog, Eric Rescorla looks into some of the privacy implications of the Federated Learning of Cohorts (FLoC), which is a Google effort to replace third-party cookies with a different type of identifier that is less trackable. But less tracking does not equal no tracking. "People's interests aren't constant and neither are their FLoC IDs. Currently, FLoC IDs seem to be recomputed every week or so. This means that if a tracker is able to use other information to link up user visits over time, they can use the combination of FLoC IDs in week 1, week 2, etc. to distinguish individual users. This is a particular concern because it works even with modern anti-tracking mechanisms such as Firefox's Total Cookie Protection (TCP). TCP is intended to prevent trackers from correlating visits across sites but not multiple visits to one site. FLoC restores cross-site tracking even if users have TCP enabled."

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