Yahoo seems to have taken a hint from Microsoft and is planning changes to its instant messaging service that could lock out users of third-party IM clients.Yahoo\u00a0seems to have taken a hint from Microsoft and is planning changes to its instant messaging\u00a0service that could lock out users of third-party IM clients.The Sunnyvale, Calif., company last week started notifying users of older versions of its Yahoo Messenger client that they have to upgrade before Sept. 24 or they will no longer be able to log on, Yahoo spokeswoman Mary Osako said Tuesday.However, the move does not affect only users of older Yahoo IM clients. As a result of the Yahoo update, third-party IM clients could also be locked out of the Yahoo IM network. Users who connect to Yahoo's network via some versions of Trillian, a popular IM client that allows users to consolidate multiple IM accounts, also are getting Yahoo's alert to upgrade each time they log on."The upgrade likely will affect third-party clients," Osako said.The Yahoo upgrade involves an update to the company's IM protocol and is meant to prevent abuse of Yahoo's network by senders of unsolicited instant messages, according to Osako."We are implementing even more aggressive measures to protect users from potential spammers. If this upgrade affects the way in which other services interact with Yahoo Messenger, it is merely a byproduct of our efforts to protect our users from potential spammers," she said.Microsoft\u00a0last month\u00a0said it is updating its MSN Messenger service in October. That update also is expected to lock out third-party IM clients. Microsoft cited a security issue, but also said it simply does not want third-party clients using its network without some form of compensation.Yahoo is open to talks with third parties about opening up the IM community, Osako said. "However, our update is not driven by a desire to establish business relationships with third parties," she said.Analysts believe Microsoft and Yahoo don't want third-party clients on their networks because they use their own clients to deliver advertisements and direct users to other services."Both Microsoft and Yahoo value the control over the clients and the last thing they want is for their users to be using third-party clients on their networks," said Michael Gartenberg, a research director with Jupiter Research.Graham Mudd, an analyst at comScore Media Metrix, agreed. "The major players see IM as a more important delivery medium and don't see any real business benefit from interoperating," he said.Yahoo Messenger users who use Yahoo Messenger for Windows 5.0 or older, Yahoo Messenger for Mac 2.0 or older, or Yahoo Messenger for Unix 1.02 or older have to upgrade, Osako said. New versions of the software are already available at\u00a0http:\/\/messenger.yahoo.com.Cerulean Studios, maker of the Trillian IM client, did not respond to a request for comment on this story.