“If you’re new to Messenger, you’ll notice that you need a Facebook account to chat with friends and close connections. We found that the vast majority of people who use Messenger already log in through Facebook and we want to simplify the process. If you already use Messenger without a Facebook account, no need to do anything.”

The change is also quietly reflected in an updated help page

It means those who took advantage of getting Messenger before the change can carry on as usual. But if for some reason you are one of the millions of people who don’t yet use Messenger, you’ll need an existing Facebook account to link it to in order to sign in.

While Facebook in its statement claims its to help users sign in easier, we suspect that the move back to the old way is to help the company knit together its huge data assets. If it can link Facebook and Messenger user data with the corresponding WhatsApp and Instagram data, it is sitting on an enviable cross section of user behaviour.

You can currently use your Facebook credentials to sign into Instagram, but not WhatsApp, which still requires a phone number and only allows sign in with one device.