From the Messenger team’s blog post today, Microsoft has announced that all users of Windows Live Messenger will be prompted to upgrade their client to the latest version (14.0.8089.726) in the following months, if not weeks, depending on your current client version:

Users currently using Windows Live Messenger 8.1 and 8.5 will be prompted to an optional upgrade starting August 25, 2009. Those who have not upgraded during this phase will receive a mandatory upgrade notice starting mid-September 2009.

Users currently using Windows Live Messenger 2009 (v14) will be prompted to an optional upgrade starting early October 2009. Those who have not upgraded will receive a mandatory upgrade notice starting late October 2009.

Users currently using MSN Messenger on Windows 2000, Windows NT 4.0, Windows 95, Windows Me or Windows 98 will not receive an upgrade notification.

Users are encouraged to upgrade their Messenger client now as those who do not administer the upgrade will not be able to sign in to Messenger after the mandatory upgrade phase. According to the blog post, the latest update provides minor code fixes, as well as addressing security vulnerabilities discussed in the Microsoft Security Advisory 973882. Those already using Windows Live Messenger 2009 (v14) will not notice any visible feature changes.

You can download the latest version of Messenger at http://download.live.com/messenger if you haven’t already done so!