Apple has refused to comment on why its DRM-free EMI tracks tag on a user's ID and email address. Instead the company has pointed to Jupiter Research analyst Michael Gartenberg’s thoughts on the matter.

Gartenberg suggests that Apple would want to tag music from the iTunes Store (something the company has always done) for a number of reasons including proof of purchase; to facilitate upgrades (to higher fidelity versions); to identify songs missing from albums (a "complete album" feature), and to thwart piracy, reports Wired.

Gartenberg wrote: “It's a pretty common practice to identify stuff like this as proof of purchase and other stores do this as well. The reasons are many why you might want to be able to tell which songs on a users hard drive came from your store for things like promotions and or upgrade offers.”

“It's hard to garner sympathy for folks concerned about uploading music to file sharing sites and being able to be found. I think the fact that you're concerned about being found might tell you that you're doing something wrong so don't do that,” he added.

However, intellectual property attorney Fred von Lohmann has suggested that the information should be encrypted. “There's absolutely no reason that it had to be embedded, unencrypted and in the clear," he told Wired. "Some of the privacy problems, in light of this, is that anyone who steals an iPod that includes purchased iTunes music will now have the name and email address of its rightful owner."

Both Gartenberg and von Lohmann expect that enterprising software developers will soon develop a way to circumvent or strip this information from the unprotected iTunes tracks.