Microsoft has opened up public access to its Messenger IM network via the Extensible Messaging and Presence Protocol (XMPP), according to an announcement at the company's Inside Windows Live blog. The use of an open standard for real-time communication means anyone will be able to build messaging clients that can access Messenger’s 300 million active users, without resorting to reverse-engineering methods.

Currently, third-party apps like Adium, eBuddy, or Pidgin connect to Live Messenger this way but they rarely support all the service's features. Although there's no indication that this will change in the short term, at least Microsoft is officilally supporting unofficial clients for the first time now.

Microsoft says that the move is motivated by its commitment to users' choice in devices and services. "With this announcement, we now have universally available protocols for accessing all our major services. There’s OAuth 2.0 for Live ID, a REST API for SkyDrive, Exchange Active Sync for Hotmail, and XMPP for Messenger."

Microsoft's instant messaging service has seen a steady drop in active users in the past two years, presumably with the rise of competing services like Facebook Chat, Google Talk or even Twitter. The former two are also based on the XMPP protocol that started life as Jabber.