"Important service announcement: As part of a recent system enhancement, we need you to change your e-mail address to continue signing in to the Windows Live Messenger Service. To ensure that your access is not blocked and to learn more, go to http://support.microsoft.com/gp/Messenger/en"
The message was sent from "email@example.com" and was actually legitimate. However was not intended to go out to the people that received the Instant Message yesterday. The Windows Live Messenger team has posted a alert for customers to please disregard the message.
The team admits that these service notifications are only used for urgent issues and that someone made an internal error that caused the message to be sent out. "We will definitely be reviewing our process to make sure we avoid such mistakes in the future" the Windows Live Team noted.