Great research started by Güneş Acar in our research group: Meta abused a loophole in Android to surreptitiously track users, violating Google's terms of service. See news article in Dutch https://nos.nl/artikel/2569805-onderzoekers-facebook-en-instagram-gebruikten-spionagetrucje-op-android-smartphones or English https://arstechnica.com/security/2025/06/meta-and-yandex-are-de-anonymizing-android-users-web-browsing-identifiers, or all the technical details in https://localmess.github.io/