didn't see this anywhere so i thought i would post it. it is build 8.1.0064Messenger Beta Tester,
We are pleased to inform you that the Windows Live Messenger 8.1 has started. We are delighted to have you on board once again and look forward to getting your feedback about the latest version of Windows Live Messenger.
Go to http://connect.microsoft.com and you will see all of the information you need to get started. Be sure to read all of the instructions and other information. It is important that you understand this information in order for you to successfully beta test this product. Additionally, there is important information about contests we will be running during the beta giving you a chance to win cool prizes!
If you have any questions or issues, you can contact the Windows Live Messenger Beta Team and email@example.com.
The Windows Live Messenger Beta Team
Source: My Inbox