Yahoo! blocks Trillian

Yahoo! has begun blocking Cerulean Studios' Trillian software from communicating with its own instant messaging software as part of its plan to limit third parties from piggybacking on its service.

On Thursday, some Trillian users began reporting an inability to communicate with their Yahoo! Messenger contacts. A Yahoo! spokeswoman on Friday morning confirmed that Trillian users' inability to access Yahoo! Messenger was the result of recent policies put in place by the web giant.

Yahoo! last week announced that it would require people who use older versions of Yahoo! Messenger to upgrade to more recent versions. Coinciding with the upgrade, Yahoo! said it would probably disable access to outside IM services such as Trillian. Yahoo! set a deadline of Wednesday for its forced upgrade and its intention to disconnect Trillian.

Yahoo! spokeswoman Mary Osako said: "If this has affected the way in which third parties interact with our service, it is merely a byproduct of our efforts to implement preventative measures to protect our users from potential spammers."

A notice posted on Trillian's website informed users about "an issue that may cause a crash or invalid password when trying to autoconnect to Yahoo!," the site read. Trillian users who reported the problem said they were unable to view their buddy lists when connecting to Yahoo!.

Scott Werndorfer, co-founder of Cerulean, said in an email statement: "We are aware of the current connectivity issues with Trillian and the Yahoo! network, brought on as a result of Yahoo!'s recent protocol upgrade. We are working hard on a solution and will update our website when more information becomes available."

Trillian software, produced by privately held Cerulean, allows people to combine various IM clients into one interface. Users can view buddy lists from various services, such as AOL Instant Messenger, MSN Messenger and Yahoo! Messenger, and exchange IM text messages with them.

The popularity of Trillian has risen, largely because popular IM services do not communicate with each other. As a result, people use different IM services simultaneously on their PCs to communicate with contacts who reside in different communities. These closed networks have helped incumbent leader AOL maintain its large market share while allowing rivals MSN and Yahoo! to flourish alongside it.

What separates the Big Three IM services are features. AOL, MSN and Yahoo! services each have distinct flavours and rely on these distinctions to maintain user loyalty. Trillian strips all clients of their differences and allows people to exchange IMs through its own look and feel.

A day after last week's Yahoo! announcement, Trillian released software patches that were aimed at allowing it to continue accessing Yahoo! and MSN buddy lists. But as of this week, those patches do not appear to be working.

Jim Hu writes for CNET News.com