MSN Messenger users sending messages to AOL users today received the following message: "You have been disconnected from the AOL Instant Message Service (SM) for accessing the AOL network using unauthorized software." It then links to a site where they can "download a FREE, fully featured, and authorized client."
The AOL message then causes the MSN Messenger client to log off, and it cannot be reactivated until the user relaunches the software.
AOL spokeswoman Tricia Primrose said the block does not affect the MSN Messenger software. Rather, it is a warning to MSN Messenger users that AOL will block access to its network of screen names.
"MSN is continually trying to work around blocks that we put in place," Primrose said. "We are blocking Microsoft, so [the new message] lets users know they are about to be blocked.
The focal point of the debate is instant messaging software popularized by AOL that allows users to send text messages to each other in real time. AOL has dominated this space by maintaining 40 million screen names in its instant messenger "Buddy List" network, and an additional 38 million registrations in ICQ, the instant messaging software it acquired last year.
The action is AOL's latest shot in its ongoing volley with Microsoft over competing instant messenger services. The battle began two weeks ago when Microsoft released MSN Messenger with a feature allowing users to communicate with AOL Instant Messenger users. AOL responded by blocking MSN Messenger from communicating with its users.
Microsoft has pushed for open standards for instant messaging, and AOL said it also supports standards. Microsoft is calling for AOL to join standard efforts outlined by the Internet Engineering Task Force. AOL, on the other hand, has asked Microsoft to join its own standards advisory board, which is staffed by top executives from AOL, Apple Computer, Sun Microsystems, RealNetworks, and Novell.