Messenger already provides end-to-end encryption on one-on-one text chats sent by users.
This means that nobody else, including Facebook, can see or listen to whats sent or said.
End-to-end encryption is already widely used by apps like WhatsApp to keep personal conversations safe from hackers and criminals.
Besides the above, Facebook has also updated controls for disappearing messages.
End-to-end encryption doesnt work for Messenger group chats and calls.
Additionally, it also plans to begin limited testing of end-to-end encrypted messages and calls for Instagram DMs.
source: www.techworm.net