Infoworld:

"Users have to upgrade to the latest versions of MSN or Windows Messenger by Oct. 15 or they will no longer be able to log on, Microsoft spokesman Sean Sundwall said. [...] Besides those older Messenger clients, the move also affects IM software such as Trillian, Imici and Odigo that allow users to consolidate multiple IM accounts in one client, Sundwall said.
"It is our expectation that those who use our service with unlicensed or unauthorized third-party clients will likely not be able to log on after Oct. 15," Sundwall said. "We would encourage those third parties to contact us to work out agreements by which they can continue to have their customers access our network." Sundwall would not comment on what type of agreement Microsoft would want with third-party IM software providers. "We are very interested in interoperating with all third parties, there just needs to be a formal agreement," he said."