Which feature introduced in 2016 secures messages end-to-end?

The feature introduced in 2016 that secures WhatsApp messages end-to-end is end-to-end encryption.

WhatsApp completed its encryption rollout on April 5, 2016, in partnership with Open Whisper Systems, the organization behind the Signal Protocol. The upgrade protected messages, group chats, photos, videos, documents, voice messages, and calls so that only the communicating users could read or hear them.

A common mix-up is two-factor authentication. Two-factor authentication protects access to an account by adding an extra verification step; it does not encrypt the contents of conversations. Disappearing messages, introduced much later, control how long messages remain visible rather than how they are transmitted.

End-to-end encryption does not mean every WhatsApp-related copy is automatically protected in the same way. Chat backups originally required separate treatment, and WhatsApp later added optional end-to-end encrypted backups for cloud storage. The 2016 milestone refers to encryption for communications within the service.