Facebook Messenger is an instant messaging service and software application which provides text and voice communication. Integrated with Facebook’s web-based Chat feature and built on the open MQTT protocol, Messenger lets Facebook users chat with friends both on mobile and on the main website. Facebook reported in November 2014 that Facebook Messenger has reached 500 million users. David A. Marcus heads Facebook Messenger and had joined Facebook on invitation of Mark Zuckerberg, CEO of Facebook.