Microsoft Corp. is making changes to its MSN instant messaging (IM) service that will lock out users of third-party software that uses the service as well as users of older versions of Microsoft's own Messenger client, the company said Tuesday.

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. The upgrade is required because of "security issues" with the older versions of the Messenger clients, he said, declining to specify those issues.

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.

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