|Initial release||August 9, 2011|
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 April 2016 that Facebook Messenger has reached 900 million monthly active users. David A. Marcus heads Facebook Messenger and had joined Facebook on invitation of Mark Zuckerberg, CEO of Facebook.
On March 17, 2015, Facebook added a functionality in which users can send money to their friends. It is currently only available in the United States.
On April 27, 2015, Facebook introduced video calling in the Facebook Messenger app. The functionality was first launched in Belgium, Canada, Croatia, Denmark, France, Greece, Ireland, Laos, Lithuania, Mexico, Nigeria, Norway, Oman, Poland, Portugal, the United Kingdom, the United States, and Uruguay.
At the Facebook F8 conference on March 25, 2015, Facebook announced that the Messenger platform is taking first steps to bring businesses on Messenger with the goal of enhancing how people and businesses communicate. Users will be able to sign up to connect with businesses in Messenger, receiving personalized updates. Businesses can use custom layouts designed for order confirmation, shipping updates and more. The service is already available with selected US businesses.
As part of this business feature, Facebook launched Transportation on Messenger in cooperation with Uber. As of January 2016, this service is still in testing and will be available to selected users in the locations where Uber operates in the United States.
In April 2016, Facebook Messenger launched "Group Calling", allowing users to add up to 50 participants simultaneously over the internet. This feature will be available on Android and iOS devices for free and users can start a group VoIP audio call from any group chat. To start a group call, a user needs to just tap the 'phone' icon, select which of the group chat members they want to include or call. All the selected members will receive a Messenger call simultaneously.
- iPhone and iPod Touch: Facebook launched the iOS version of Facebook Messenger on August 9, 2011.
- iPad: On July 3, 2014, a native Facebook Messenger app was released for iPad. It was specially designed for iPad rather than just running as an enlarged iPhone app. Messenger for iPad features a multi-window interface showing a list of threads and the current conversation at the same time.
- Android: Facebook launched the Android version of Facebook Messenger on August 9, 2011.
- In December 2012, the Facebook Messenger app for Android in some regions (such as Australia, South Asia, Indonesia, South Africa, and Venezuela) added the ability to use Messenger without a Facebook account by simply using a name and phone number. These changes are intended to allow Facebook Messenger to compete against similar mobile messaging platforms such as WhatsApp as an alternative to text messaging. Later updates added the ability to use Facebook Messenger as a replacement text messaging client on Android, and added "Chat Heads", an overlay chat system originating from Facebook Home.
- BlackBerry OS: Facebook launched the BlackBerry OS version of Facebook Messenger on October 11, 2011.
- Windows Phone 8: On March 5, 2014, Facebook Messenger app was released for Windows Phone 8. This app contains many features similar to iOS and Android apps but lacks chat heads and voice messaging features.
- Web: On April 8, 2015, Facebook officially launched messenger.com, which enables users to chat directly through a web browser, without needing to visit facebook.com. Facebook stated that the messages feature in facebook.com will not be removed, unlike how Facebook has separated the feature in its mobile app.
- Windows 10: In May 2016 Facebook launched a fullly featured messaging app for Windows 10.
- Microsoft Windows: Messenger for Windows Desktop was officially released on March 5, 2012 for Windows 7 users. Testing on the software began among a limited beta tester group on November 21, 2011; however, a leaked link to the beta-stage software was publicly revealed to tech bloggers by Israeli blog TechIT. Facebook responded the same day by announcing the link's availability through its Help Center.
- Among its features was a "ticker" similar in function to the sidebar of friend activity seen by Facebook website users. At the time of release, "chatting with multiple friends, video calling, limiting chat availability and editing settings" were not available through the software. A Mac OS X version was mentioned by Facebook developers as forthcoming. Messenger for Windows Desktop was discontinued on 3 March 2014.
- Firefox: Facebook also launched an add-on for Firefox, titled Facebook Messenger for Firefox. Facebook Messenger for Firefox was discontinued on 3 March 2014.
Facebook Messenger supports chatbots, and in April 2016 launched a Messenger Platform service which allows developers to create bot accounts that can interact with Facebook users. Bots created at launch include weather services, CNN news, 1-800-Flowers and the interactive fiction adventure Zork.
In May 2016, Facebook announced an encrypted version of its Messenger bot. 
The Electronic Frontier Foundation (EFF) has listed Facebook Messenger (Facebook chat) on its Secure Messaging Scorecard. As of November 6, 2014[update], Facebook Messenger has a score of 2 out of 7 points on the scorecard. It has received points for having communications encrypted in transit and for having recently completed an independent security audit. It is missing points because the communications are not encrypted with keys the provider doesn't have access to, users can't verify contacts' identities, past messages are not secure if the encryption keys are stolen, the source code is not open to independent review, and the security design is not properly documented.
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