The Mac maker forces a developer to stop distributing a plug-in that turned its iTunes music player into peer-to-peer music-sharing software.
The plug-in, called iCommune, allowed iTunes users to browse the music libraries of other Macintoshes over a network and stream or download music from them.
On Wednesday, Apple notified developer James Speth that he was violating the terms of his software agreement and ordered him to stop distributing the plug-in and to return Apple's development tools. Speth removed the iCommune download from his Web site.
Apple's move comes amid increasing hostility between the entertainment industry and music-swapping applications such as Kazaa and the now-defunct Napster.
However, Apple did not make any direct reference to copyright issues in pulling the plug on iCommune. Instead, the company said that Speth broke the terms of the agreement that allowed him access to the iTunes software development tools. Apple makes those tools available to those that want to make their hardware compatible with iTunes but not to software makers that want to tap into iTunes.
"The iTunes (software developer) materials are licensed only for the purpose of enabling the licensee's hardware device identified in the agreement to interoperate with iTunes," Apple said in its letter to Speth. iTunes "is not licensed for use in a software program for sharing of music over a network." An Apple representative declined to comment on the matter.
In an e-mail interview, Speth said he first started working on iCommune in April 2002 as a way to have his iTunes library talk to a Linux-based machine that was connected to his stereo. In the fall, he started working on a broader release that he finished just in time for this month's Macworld Expo.
"I had been using a Web interface to control that system, but then I thought of getting iTunes to interface with it," Speth said. "Having the music on that system show up in the iTunes setup on my laptop sounded ideal."
Speth said that the conflict with Apple was the result of a misunderstanding.
"Unfortunately, iCommune grew beyond the scope of what I had originally described to Apple in the license agreement, and they've asked me to stop distributing it," he said.
Speth said he hopes to make iCommune work without using Apple's intellectual property.
"If I can rework it to not need the Apple-licensed code, then I'll go back to distributing it," he said. "Or if it turns out that the license is unnecessary or not legally binding, I'll continue work on it. But right now I'm taking stock of the situation before making it available again."
Apple is known for keeping a watchful eye on developers who extend the functionality of its applications and its Mac OS X operating system. Last August, the Mac maker threatened to invoke the Digital Millennium Copyright Act against a developer who patched iDVD to allow it to burn movies to external DVD drives.
Apple has also been leveraging iTunes in its own software development efforts.
The company has built features into new versions of several of its other programs--iDVD, iPhoto and iMovie--that allow them to access music from iTunes. In a keynote speech last July, Apple Chief Executive Steve Jobs demonstrated a feature similar to that provided by iCommune to be included in a forthcoming version of iTunes. In introducing Rendezvous, Apple's technology for allowing software and devices to automatically discover each other over a network, Jobs showed iTunes running on a desktop computer playing music from an iTunes library on a wirelessly connected laptop. Apple has said such functions would be added to iTunes early this year, but no further details have been announced.
ZDNet U.K.'s Matthew Broersma reported from London, and News.com's Ian Fried reported from San Francisco.