Microsoft is contacting providers of instant messaging (IM) software to try to cut licensing deals before stops its MSN IM network.
Microsoft is targeting makers of clients that use the Microsoft MSN IM network and compete with Microsoft's own MSN Messenger.
Cerulean Studios, maker of the Trillian IM client, allows 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.
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Trillian has been downloaded more than 10 million times, according to Cerulean Studios.
"Running an [IM] network is expensive," said 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 unauthorised third-party clients".
The first phase of those changes is scheduled to go into effect mid-September, followed by a complete lock-out on 15 October.
Trillian maker Cerulean Studios is interested in signing a deal with Microsoft, the company's co-founder and head developer Scott Werndorfer said.
"We're anxious to work with Microsoft on any licensing models they might have," Werndorfer said.
He added that Trillian Pro 2.0, which entered beta testing on 1 August, supports the latest MSN IM protocol, but did not say if that means that older Trillian clients will be locked out from the MSN IM network soon or if Trillian Pro 2.0 would work with MSN IM regardless of a licensing deal.
Other clients that connect to Microsoft's IM network include Imici and Odigo.
The changes to the MSN IM network also are for security and privacy reasons, Microsoft said.
"If there is unauthorised access to our network, it opens us up to potential security and privacy vulnerabilities," Gurry said.
However, there is a yet undisclosed security flaw in Microsoft's IM network and clients.
The flaw is forcing users of several older versions of its own MSN Messenger and Windows Messenger clients to the upgraded versions. Users who have to upgrade have been alerted via e-mail and will soon start to see notifications in their Messenger client
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 and providers have also added video conferencing, PC phone calls, gaming and other features.
Joris Evers writes for IDG News Service