Snoops and spooks will be shut out of messages sent by the more than half a billion WhatsApp users around the world.
WhatsApp has turned on a new encryption system developed by the secure communication group Open Whisper Systems.
Data will be scrambled as it's sent from user to user, and will be switched on as a default setting.
Tech firms have recently been criticised by security agencies for failing for encrypting messages and failing to cooperate.
Earlier this month GCHQ director Robert Hannigan pointed the finger at “large US tech companies”, and explicitly mentioned WhatsApp as facilitating terrorism.
Yet WhatsApp’s latest move “represents the largest deployment of end-to-end encryption communication in history”, said Open Whisper Systems in a blog post today. WhatsApp has around 600m monthly active users worldwide.
The encryption service is currently only available for text messages on Android devices, and does not cover group chats or media messages. Further updates are in the works.
The encryption system incorporates Open Whisper Systems’ own private messaging service TextSecure.
WhatsApp was bought by Facebook for $21.8bn in October this year. At the time the app’s founder Jan Koum downplayed security concerns in a blog post in which he claimed “respect for your privacy is coded into our DNA.”