Google's FLoC (Federated Learning of Cohorts) mechanism for ad personalisation, currently being trialled in the Chrome browser, has been rejected as privacy-invasive tracking by other browser makers including Vivaldi and Brave.
FLoC is part of what Google calls the Privacy Sandbox initiative, a proposal to "support business models that fund the open web in the absence of tracking mechanisms like third-party cookies," according to Chrome engineering director Justin Schuh and product manager Marshall Vale.
Third-party cookies are widely used (or abused) for tracking users across the web, and are increasingly likely to be blocked. Google is determined to preserve its ability to target and personalise advertising and claims the Privacy Sandbox APIs "enable use cases such as ad selection and conversion measurement, without revealing individual private and personal information."
Diagram via web.dev/floc/ (click to enlarge). Licensed under CC 4.0
The idea of FLoC is that each web browser has a cohort ID which groups it with other browsers that have a similar browsing history. Google runs a FLoC service that defines the cohorts and sends data to the browser. The cohort ID is then calculated by the browser. The browser does not send its history to the FLoC service.
Websites can query the browser for its cohort ID and select advertising accordingly. Advertising networks – such as Google's own – are expected to record data such as "a browser from cohort 1354 showed interest in hiking boots." It is profiling, but of groups rather than individuals.
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