As a result of the attack, hackers were able to log in to the victim’s account from another device, or simply find out that the owner of such and such phone number uses Signal.Among these 1900 numbers, the attackers were interested in three specifically, whereupon Signal was notified by one of these three users that their account had been activated on another device without their knowledge.On the pages of Kaspersky Daily, we have often talked about the fact that Signal is a secure messenger, and yet it was successfully attacked.This mechanism allows the Signal app on your phone to send encrypted information about contacts and receive a likewise encrypted reply as to which of your contacts uses Signal.The app contains a feature called Registration Lock (to activate go to Settings → Account → Registration Lock), which requires a user-defined PIN to be entered when activating Signal on a new device."