The Apple checksum was quickly reverse-engineered, allowing those other music-playing applications to be used with Apple's devices. Recently, however, Apple shipped new versions of the iPhone and iPod touch that use a new crypto technique that has not been cracked. That's what the engineers were discussing on Bluwiki, von Lohmann said.

"Although it doesn't appear that the authors had yet figured out the new iTunesDB hashing mechanism, Apple's lawyers nevertheless sent a nastygram to the wiki administrator," he wrote.

Neither Apple nor O'Melveny & Myers responded to requests for comment for this story.

In an Interview, von Lohmann said Apple was using the DMCA to stifle free speech. "Apple is essentially saying here that people can't even talk about the mechanisms that Apple uses to lock in its music to the iTunes software," he said.

The checksum mechanism does not protect copyright on iTunes music; it's just supposed to confirm that the iPhone is communicating with iTunes, he added. "Nobody has ever suggested a purpose of this other than forcing iPod owners to use Apple's software," he said. "It's an anticompetitive tie-in device."