Adblock Filters Expose User Location Even With VPN Protection

Adbleed is a client-side fingerprinting method that probes domains unique to country-specific adblock filter lists and detects whether requests are blocked almost instantly or allowed to reach the network; by correlating which regional lists are active, an attacker can infer a user's country or language even when they use a VPN, Tor, or proxy. The report describes the detection technique, privacy impacts, and mitigation ideas (disable country lists, randomize lists, or apply rules more selectively).