The first audio compact disc to be sold in Japan with copy protection went on sale today as the country's major consumer electronics makers looked on, concerned that the discs might cause confusion among consumers.

Avex, one of Japan's largest record labels, is the first domestic CD maker to employ copy protection with popular female singer Boa's latest single, Every Heart - Minna no kimochi. This technology could easily find its way on to CDs worldwide.

The company said it decided to use the technology in response to recent developments in computer and telecommunication technology that have made it easier than ever to obtain music for free.

"We have added copy protection to the disc for two main reasons," said Toshihide Yamada, a spokesman for Tokyo-based Avex. "The first is a rapid increase in the popularity of P-to-P [peer-to-peer] file sharing software. When Napster was around, it was only available in English so not that many people accessed it [in Japan] but last year a Japanese website for FileRogue was developed and the number of users has exploded.

"The second reason is that more and more school children are buying secondhand CDs, taking them home, copying them and then returning them to the CD store," he said.

The price of PCs with CD writers has dropped and having a CD-RW in a PC is now a basic necessity. CD-R disc prices have also fallen sharply.

The Boa disc uses the Cactus Data Shield copy protection system developed by Israel's Midbar Tech and can only be played back on audio CD or DVD players.

Playback is not possible on most MP3 CD players and car navigation systems, while personal computer users, though not locked out of the disc, have to use a player installed on the disc. Standard CD player software cannot access the disc and the player works only on the Windows operating system.

Such restrictions have consumer electronics companies and computer makers wary of the new technology, particularly because in the last year these companies have started to push PCs that seek to act as replacements for music systems, televisions and video recorders.

Of particular worry to these companies is whether the copy-protected CDs, because of the system employed, are actually in compliance with the CD specification.

Sony, one of the companies that developed the CD format, has just such concerns.

"If these copy-protected CDs go out into the market, they have to be clearly labelled as such," said Gerald Cavanagh, a spokesman for Sony in Tokyo. "When they are produced, they have to be clearly labelled to consumers that these are not standard audio CDs, that there are certain limitations on the kind of devices they can be played on and that they do not necessarily conform to the existing CD audio standard."

The appearance of copy protection on the discs has done nothing to stop piracy of the new single, however. Its existence on an album, which has no such technology, and promotional radio and TV airplay has led to the song already appearing on file sharing systems. The bigger test of the copy-protection technology will come later this month when it appears on two albums that contain songs which are, as yet, unreleased.