Facebook isn't the first company you think of when privacy comes to mind. Nor is it second, third, or anywhere near the top dozen. It's lucky if it's anywhere on the list at all. But the company does own WhatsApp, the widely used instant messenger that started encrypting all messages earlier this year. Now Facebook is testing out that same encryption in Messenger.
Facebook Messenger is using the same protocol that Open Whisper Systems developed for TextSecure and, later, Signal. Unlike WhatsApp or Signal, Facebook isn't encrypting all messages. Only those conversations that you and another person deem secret will disappear from prying eyes. It's the approach we've seen taken by various secure messaging services for years, and it's the same path Google is taking with Allo.
Secret conversations come with limitations. The big one is that messages can only be read on one device. These conversations also don't support GIFs or videos. And don't bother trying to send money anonymously, as it's not going to happen.
The test is limited for now, but Facebook plans to make the feature widely available later this summer.