Windows Live Messenger (formerly MSN Messenger) is a deprecated instant messaging client developed by Microsoft for Windows, Xbox 360, Blackberry OS, iOS, Java ME, S60 on Symbian OS 9.x and Zune HD.[1] It connected to the Microsoft Messenger service while also having compatibility with Yahoo! Messenger and Facebook Messenger. The client was first released as MSN Messenger on July 22, 1999 and was marketed under the MSN branding until 2005 when it was rebranded under Windows Live and has since been officially known by its present name, although its previous name was still used colloquially by most of its users.[2][3] In June 2009, Microsoft reported the service attracted over 330 million active users each month, placing Messenger among the most widely used instant messaging clients in the world.
Following the acquisition of Skype Technologies, Microsoft began to promote Skype and introduced the ability to merge their Skype accounts with a Microsoft account, allowing users to communicate with Messenger contacts via Skype, which had additional features and a wider user base. This started the discontinuation dispute.

Before the product was renamed Windows Live Messenger, it was named "MSN Messenger" from 1999 to 2006. During that time, Microsoft released seven major versions as follows. The first version of MSN Messenger Service, version 1.0 (1.0.0863), was released July 22, 1999. It included only basic features, such as plain text messaging and a simplistic contact list.[4] When it was first released, it featured support for access to America Online's AIM network. America Online continually tried to block Microsoft from having access to their service until eventually the feature was removed, and it has not re-surfaced in any later versions of the software.[5] AOL did this by exploiting a buffer overflow bug in AIM, which causes it to execute a bit of machine code sent by the server. When this code runs, it determines if the client is AIM and sends a message back to verify the client.[6] Since then, the software has only allowed connections to its own service, requiring a Windows Live ID (.NET Passport at that time) account to connect. Microsoft released the first major update, version 2.0 (2.0.0083), on November 16, 1999. It included a rotating advertising banner and the ability to customize the appearance of the chat window. It came as an install option for Windows Me. This version was followed the next year by version 3.0 (3.0.0080), which was released May 29, 2000. It included file transfers and PC-to-PC and PC-to-phone audio capabilities with Net2Phone, one of the first VOIP providers