The popularity of Apple's iTunes Music Store is forcing Microsoft to improve its DRM music-sharing technology.

Most online-content providers employ the most recent iterations of Microsoft's Windows Media DRM system, which has not supported Macs since version 1, leaving Mac users unable to access many existing music download services.

Microsoft licensees - such as the UK-based OD2 network - have so far failed to achieve the kind of market traction Apple's service enjoys. Apple's three million song downloads eclipses activity across the rest of the industry. This has led many to dismiss subscription-based services in favour of Apple's pay-per download service.

Other consumer-friendly features that Microsoft plans to introduce include support for a technology that would track if users were paying their subscription fees - even when legally-acquired tracks were hosted on MP3 players. If customers don't pay, Microsoft simply cuts off access to the subscribed-to music collection.

OD2 director of sales and marketing Edward Averdieck said: "The labels have insisted on the level of DRM offered by Microsoft. We are looking at alternatives, but working with multiple forms of DRM only makes sense if the market is there."

"Many of our shareholders are very pro-Mac. We hope to make our service Mac-compatible, but we are in the hands of our technology provider, Microsoft." OD2 was founded with investment capital from renowned Mac user, the musician Peter Gabriel.