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It had been only available to Android smartphone users in 2014.

Other services like Signal, Wickr and Telegram use end-to-end encryption. Google, Facebook and Yahoo use some encryption to protect emails and messages while they are transferred. But the messages can be unlocked by the companies under court order, the AP reported.

WhatsApp works differently because the encryption encodes each message that can only be unlocked by the sender and recipient.

It also provides a security code that senders and recipients can use to verify a message came from an acquaintance, not a hacker posing as someone they know.