Spying Chrome Extensions: 287 Extensions spying on 37M users

Using a leakage metric we flagged 287 Chrome extensions that exfiltrate browsing history. Those extensions collectively have ~37.4 M installations – roughly 1 % of the global Chrome user base. The actors behind the leaks span the spectrum: Similarweb, Curly Doggo, Offidocs, chinese actors, many smaller obscure data‑brokers, and a mysterious “Big Star Labs” that appears to be an extended arm of Similarweb.