In the latest example of a potentially market-defining patent being granted without fanfare, AOL Time Warner quietly has become the owner of a patent, granted in September by the U.S. Patent and Trademark Office, that covers much of the technology behind instant-messaging services. Patent No. 6,449,344 appears to be a far-reaching one, with more than 200 claims that give AOL exclusive rights to a "communications system for facilitating locating a user who is connected to a communications network, preferably for the purposes of establishing point-to-point communications."

The application for the patent was filed in 1997 by Mirabilis, the Israeli firm that invented the popular ICQ IM system that later was acquired by America Online, at which point ownership of the patent application transferred to AOL.

It's unclear what AOL Time Warner plans to do with the patent, but it could potentially either cut licensing deals with other IM providers that want to continue using the technology, or it could file patent-infringement suits. An AOL Time Warner spokesman declined to comment, except to say the company hasn't made any decisions on how to exercise its rights to the technology. Officials at Yahoo and Microsoft, which provide the two most popular IM services after AOL's market-leading Instant Messenger, also declined to comment.

Among the elements of an instant-messaging system that are protected by AOL's patent are presence awareness, or the ability to detect another user's online availability; the concept of the buddy list, which lets users create a list of other users for the purpose of monitoring their presence; the ability to shield one's presence from particular users; and the practice of notifying users when members of their buddy lists log on or off.

Microsoft and AOL have recently embarked on a project to develop secure chat applications for corporate users, the first major effort to cash in on what has been a largely free software tool.

AOL has scores of other technology patents, including one for Internet-browsing memory tags, or cookies, and another for Secure Sockets Layer, an application that secures E-commerce transactions. But it has never sought to enforce these.

However, it has been very protective of its IM technology. It didn't permit rivals' proprietary IM applications to communicate with its own AOL Instant Messenger and ICQ for years, although it now allows this in a limited fashion.

But Michael Sampson, an analyst with Ferris Research, says the patent isn't as solid as it might appear. In the 1980s, MIT developed the so-called Zephyr instant-notification service that offered many of the same capabilities of IM and could be used to prove that something similar existed a decade before ICQ. That's why Sampson says of AOL's patent, "I don't believe it is enforceable."