The phenomenon of Microsoft enforcing mandatory updates to MSN/ Windows Live Messenger are not uncommon. Although much of these are claimed to be "security" focused, there is the case that Microsoft rightly prefers users to be using the latest protocol their client can communicate with to avoid server issues. Still, for many users using older versions of Messenger, this is a pain as there is a significant amount of people choosing to use an older, outdated build. Below is a breakdown of the current schedule of mandatory upgrades coming within the next couple of months:

• August 25th: Message displayed to users using versions 8.1 and 8.5 to optionally upgrade
• Mid-September: Those using versions 8.1 or 8.5 will be locked out of the Messenger service and forced to upgrade
• Early-October: Users using an outdated version of Windows Live Messenger 2009 will receive the option to upgrade
• Late-October: Those using older versions of Windows Live Messenger 9 will be locked out of the Messenger service and forced to upgrade

To conclude, this series will stop users normally being able to sign into Windows Live Messenger versions 8.1 and 8.5, while also making those who haven't updated to the second QFE patch to do so by the end of October.

Source: The MessengerSays blog