Social media giant Facebook has announced that its Messenger service will now require users to sign up first to Facebook, and then to the messaging platform. Back in 2015, Facebook let users sign up to Messenger using only their phone numbers, but that process has been changed since it believes "the vast majority of people who use Messenger already log in through Facebook". While the rule is applicable only to new users attempting to use the service, some existing users have reportedly faced trouble while signing in, with the app telling them their account has been restricted. The tech giant recently updated its trio of main apps--Facebook, Messenger and WhatsApp--to include the company's new branding.