Instagram and Messenger could soon follow WhatsApp in introducing encrypted messaging as part of Facebook's plan to unify its app empire. In the meantime, WhatsApp is adding an extra layer of privacy on iOS with support for Touch ID and Face ID. The update (version 2.19.20) allows users to lock their messages behind their iPhone's biometric authentication features. You can switch it on by heading in to settings, selecting Account, Privacy and "enable Lock Screen." You'll then be able to set a time limit immediately, after a minute, 15 minutes or 1 hour.