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Microsoft is contacting providers of instant messaging software to try to cut licensing deals before it boots the clients from its MSN instant messaging network.

Microsoft isn't targeting rival IM network operators such as America Online or Yahoo. Rather, the software giant is seeking licensing fees from the makers of clients that use the Microsoft MSN IM network and compete with Microsoft's own MSN Messenger client.

Target: Trillian

Cerulean Studios, maker of the Trillian IM client, is at the top of Microsoft's hit list. Trillian enables users to consolidate multiple IM accounts in one client and is available in a free version, as well as a $25 Pro version that offers additional features. Trillian has been downloaded more than 10 million times, according to Cerulean Studios.

"Running an [IM] network is expensive," says Lisa Gurry, group product manager for MSN at Microsoft. "We can't sustain multiple other-people's businesses, particularly if they charge for certain versions of their software. We're introducing licensing processes for third parties like Trillian."

Microsoft is making changes to its network that will lock out "unlicensed or unauthorized third-party clients." The first phase of those changes is scheduled to go into effect mid-September, followed by a complete lockout on October 15, Microsoft says.

Cerulean Studios is interested in signing a deal with Microsoft, says Scott Werndorfer, the company's cofounder and head developer, in an e-mail response to an inquiry.

"We're anxious to work with Microsoft on any licensing models they might have," Werndorfer says. Trillian Pro 2, which entered beta testing on August 1, supports the latest MSN IM protocol, Werndorfer adds. He does not say whether older Trillian clients will be locked out from the MSN IM network soon, or whether Trillian Pro 2 will work with MSN IM regardless of a licensing deal.

Other clients that connect to Microsoft's IM network include Imici and Odigo.

Security Cited

Besides the issue of not wanting to let other client makers exploit its messaging network, Microsoft says it has other reasons to change the MSN IM network, citing unspecified security and privacy concerns.

"If there is unauthorized access to our network, it opens us up to potential security and privacy vulnerabilities," Gurry says. In fact, there is a yet-undisclosed security flaw in Microsoft's IM network and clients, she adds.

Because of this unrevealed flaw, Microsoft is forcing users of several older versions of its own MSN Messenger and Windows Messenger clients to upgrade to newer versions. Users who must upgrade have been alerted via e-mail and will soon start to see notifications in their Messenger client, according to Microsoft.

The battle over IM interoperability is ongoing. AOL periodically revamps AOL Instant Messenger so that Trillian users cannot access its network.

MSN Messenger is one of the most popular IM services on the Internet, along with AOL's Instant Messenger and Yahoo's Messenger. Microsoft claims about 100 million unique users log on to its service each month. IM services let users exchange text messages in real time; providers have also added videoconferencing, PC phone call capabilities, games, and other features.