Apple has long used its two-step verification system to verify Apple ID accounts when signing into new devices, but it looks like the company has now extended the security feature to cover iMessage and FaceTime.
if users log out of their FaceTime or iMessage accounts and attempt to log in again, or log in on another machine, they will require a security code to confirm their username and password.
Apple originally enabled two-step verification for iCloud accounts back in March of 2013. However, the service was restricted to things such as making account changes and signing in on new devices. Its extension to FaceTime and iMessage should hopefully make both services much more secure going forward.
Bear in mind that we haven't seen official word from Apple on this yet, so it may not be immediately available to everyone.