The new iMesh, launched last week as the first record label-approved file-swapping service, has a Led Zeppelin problem.

Like its peers in the digital music business, from Napster to Apple Computer's iTunes, iMesh does not have the legal rights to distribute recordings from the popular 1970s rockers. But using the company's new service, it requires only a quick point and click of the mouse to download several of Led Zeppelin's biggest hits.

In a sample of searches performed by CNET News.com, the same was true of songs from Green Day's latest album, a handful of tunes from The Black Eyed Peas, and other copyrighted works--precisely what the company's new filtered file-swapping model was created to avoid.

It is far too early to say whether this is a serious flaw, or bugs that will be cleaned up in just a few days of frantic code-tweaking. But the continued availability of copyrighted tunes on the iMesh network shows just how high the hurdles remain for this ambitious experiment with legal file swapping.

"We don't see this as a long-term challenge," said iMesh Executive Chairman Bob Summer. "Given that we're in an early beta phase technology, issues are to be expected. These are isolated problems which we are diligently working on fixing."

iMesh carved out a unique role for itself last year, as the first formerly unregulated file-swapping network to settle a copyright lawsuit with the big record labels that included a deal allowing it to transform itself into a "legitimate" music service.

The Israeli company agreed to pay the labels $4.1 million, and in return it was allowed to continue operating unmolested while it developed a new version of the service that would filter out copyrighted works and sell users individual songs or monthly subscriptions instead.

The company adopted song-recognition technology from Audible Magic that helps it identify songs as they are being downloaded, by comparing an audio "fingerprint"--essentially a digital representation of a song's sonic characteristics--against the known signatures of copyrighted songs. It tapped MusicNet, a wholesale digital music service that feeds Yahoo, AOL and other rivals, to provide the back end for the iMesh subscription.

MusicNet's catalogue of more than 2 million songs was also used to help create the master database of audio fingerprints, along with information directly from labels for songs not yet in MusicNet's files.

The new service, which launched early last week, allows people to download subscription versions of more than a million songs that will be free for a month or two, but which will require a payment of $6.95 a month to listen to afterward. But it allows people to search the unregulated file-swapping network for other noncopyrighted songs, and this is where the glitches lie.

The new service is supposed to identify unprotected versions of the record labels' copyrighted works as they are being downloaded, and block them before they reach a computer's hard drive. In many, if not most, cases this works flawlessly. However, works by Led Zeppelin, Green Day, Franz Ferdinand and others slipped through the filters seemingly without problem.

iMesh co-founder Talmon Marco said that some of the songs slipping through may be because the service does not yet have fingerprints on hand from record labels, or is still in the process of analyzing the fingerprints. The company does have a process in place to let record labels claim tracks, which will let those tracks be blocked in the future, he said.

The issues are reminiscent of the last major experimentation with installing filters on an active file-swapping service, when a federal court ordered the original Napster to block illegal swapping on its network in 2001.

That company installed an early generation of filters that was easily evaded by the user base, and was subsequently criticized harshly by the courts. A subsequent generation of filters cleaned virtually everything off the network, and the company shut down the service not long afterward.

Representatives of record labels and music publishers contacted about the new iMesh service declined to comment, but said they were continuing to look at the issue.