Popular messaging service WhatsApp may be the most secure of all, as it just added end-to-end encryption to further boost security.

More specifically, WhatsApp has implemented end-to-end encryption with a recent update for its Android app. Unlike similar forms of communication on Facebook, Google, and other major networks and services, WhatsApp is unable to decrypt messages even if they have to. In other words, even if WhatsApp is pressured or forced to decrypt messages for legal reasons, it cannot do so.

Many consider end-to-end encryption to be the strongest form of encryption available on any major messaging service, and WhatsApp may be the most secure service of its kind.

In order to offer the new security feature, WhatsApp has joined forces with open Whisper Systems, which received high praise for its TextSecure program. While Open Whisper Systems developed a number of relevant apps, TextSecure stands out from the crowd by using forward secrecy to keep messages encrypted even if the key is compromised.

Getting TextSecure ready for WhatsApp took roughly six months, but it is now ready to grace the service's massive Android user base. It remains unclear for now just when the feature will be available for the iOS version of WhatsApp as well, but Open Whisper promised to keep working on such efforts.

"Today we're excited to publicly announce a partnership with WhatsApp, the most popular messaging app in the world, to incorporate the TextSecure protocol into their clients and provide end-to-end encryption for their users by default," Open Whisper Systems announced in a company blog post on Tuesday, Nov. 18.

"The most recent WhatsApp Android client release includes support for the TextSecure encryption protocol, and billions of encrypted messages are being exchanged daily. The WhatsApp Android client does not yet support encrypted messaging for group chat or media messages, but we'll be rolling out support for those next, in addition to support for more client platforms. We'll also be surfacing options for key verification in clients as the protocol integrations are completed."

Open Whisper Systems further adds that a full deployment of Text Secure will be an incremental process for WhatsApp's impressive number of mobile platforms, but TextSecure protocol support will eventually reach each WhatsApp client platform.

"We have a ways to go until all mobile platforms are fully supported, but we are moving quickly towards a world where all WhatsApp users will get end-to-end encryption by default."

Considering that WhatsApp has more than 600 million users on its network, this marks the largest end-to-end encryption deployment.