Russian cyberwarfare has been using Ukraine as a test lab for its latest hacking techniques, and now Google is warning of a Russian espionage trick that's been used to obtain Ukrainians' messages on the encrypted platform Signal. The trick involves sending phishing messages with fake QR codes that link the victim's phone to a new device, allowing hackers to read every message the target sends or receives. Signal has pushed out an update to counter the trick, warning users when they link a new device and checking with them again at a randomized interval to confirm that they still want to share all messages with it. The update also requires a form of authentication, such as entering a passcode or using FaceID or TouchID on iOS, to add a new linked device.