Protocol
Windows Live Messenger uses the Microsoft Notification Protocol (MSNP) over TCP (and optionally over HTTP to deal with proxies) to connect to Microsoft Messenger service—a service offered on port 1863 of "messenger.hotmail.com."
The protocol is not completely secret; Microsoft disclosed version 2 (MSNP2) to developers in 1999 in an Internet Draft, but never released versions 8 or higher to the public. The Messenger service servers currently only accept protocol versions from 8 and higher, so the syntax of new commands sent from versions 8 and higher is only known by using packet sniffers like Wireshark. This has been an easy task because – in comparison to many other modern instant messaging protocols, such as XMPP – the Microsoft Notification Protocol does not provide any encryption and everything can be captured easily using packet sniffers. The lack of proper encryption also makes wiretapping friend lists and personal conversations a trivial task, especially in unencrypted public Wi-Fi networks.
Read more about this topic: Games And Applications For Windows Live Messenger