Google's replacement for FLoC, known as the Topics API, faced similar criticism from various groups. Mozilla pointed out flaws in the Topics API's design, highlighting that it could allow large advertising networks to reidentify and track users by aggregating their interests across numerous websites. Apple echoed similar concerns, also noting that the proposal contradicted efforts made by other browsers to partition data on a per-site basis. Furthermore, when the proposal was initially announced, there were uncertainties about how Google or other browser vendors would establish a taxonomy of topics, a critical aspect of the API that was left underspecified. Alongside the Topics API, Google's other proposals within the Privacy Sandbox, such as Client Hints, have also sparked significant privacy concerns among other browsers. These concerns primarily revolved around the potential for Client Hints to expand the surface area for passive fingerprinting on browsers.
Due to Google's ownership of the browser with the largest market share, concerns have been raised about the anticompetitive nature of its proposals. Consequently, in January 2021, the Competition and Markets Authority (CMA) in the United Kingdom announced plans to investigate the Privacy Sandbox initiative, with a focus on its potential impacts on both publishers and users. CMA subsequently accepted legally binding commitments offered by Google concerning its proposals to remove third party cookies on Chrome and develop the Privacy Sandbox. The formal acceptance of these commitments by the CMA resulted in the closure of the investigation, with no decision on whether the Competition Act 1998 was infringed. CMA reported that Google was complying with its legally-binding commitments between July 2022 and September 2022. In March 2021, 15 attorneys general of U.S. states and Puerto Rico amended an antitrust complaint filed the previous December; the updated complaint says that Google Chrome's phase-out of third-party cookies in 2022 will "disable the primary cookie-tracking technology almost all non-Google publishers currently use to track users and target ads. Then [...] Chrome, will offer [...] new and alternative tracking mechanisms [...] dubbed Privacy Sandbox. Overall, the changes are anticompetitive". The lawsuit suggests that the proposed changes in the Privacy Sandbox would effectively require advertisers to use Google as a middleman in order to advertise.
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