PSA: Anyone can tell if you are using WhatsApp on your computer

A security researcher (Tal Be’ery) demonstrated that WhatsApp’s multi-device design leaks device-presence metadata: by creating distinct session keys per device, senders can determine whether a recipient is using only the mobile app or also web/desktop clients. The leak can be observed by anyone who knows the target’s WhatsApp number (even after being blocked) and could assist stalkers or attackers in profiling targets; Meta says the behavior is intentional to support multi-device encrypted messaging.