Facebook has a new Messenger app you'll need to download right away if you message your friends on Facebook using your cell phone.
In fact, Facebook says it's been sending users this warning because in just a few days you won't be able to message people using the main Facebook app.
Facebook says Messenger is already used by more than 200 million people every month. The goal is to turn Messenger into an important business.
The good news is you'll be able to message friends about the same way you do now. Once you install the app, just tap the message icon, and it will take you to Messenger automatically.
To go back, just hit the "return to Facebook" icon.
Facebook says every month it has more than one billion active users around the globe.