Facebook is testing a "Secret Conversations" encrypted message feature.

Just like on WhatsApp and Apple's iMessage, Facebook is about to bring end-to-end encryption to its Messenger app.

However, for the moment at least, the feature, which Facebook is calling "Secret Conversations," is in the testing stage and so will be open initially to a small test group.

Explaining the reasoning behind the new feature, Facebook said that the Secret Conversations setting is something users will be able to activate in those instances "When you want additional safeguards -- perhaps when discussing private information like an illness or a health issue with trusted friends and family, or sending financial information to an accountant."

The feature is for text messages only -- it won't support videos or gifs, and each message can only be viewed on a single device. If a recipient reads the message on his or her smartphone, they won't be able to access it via the desktop or a tablet.

There's also an element of Snapchat about it. The sender can set a time limit in terms of how long a message remains viewable or readable.

It will not be a default setting, you will have to manually select the feature when sending a message.