Mark Zuckerberg is on Signal, reveals security expert A security researcher disclosed it posting the details using Zuckerberg's leaked phone number and Facebook data Facebook Hits Blocks News in Australia Over Media Bargaining Law When Facebook CEO Mark Zuckerberg's phone number was leaked along with 533 million Facebook users in the biggest data leaks ever, other details of him came to light, surprising many. Zuckerberg's details such as his name, birth date, location, marriage details, and Facebook user ID led to the revelation that the Facebook CEO uses the Signal app. A security researcher disclosed it posting the details using Zuckerberg's leaked phone number.