With ever more songs, pictures and video clips being sent over the airwaves to mobile phones, Microsoft plans to beef up its investment in DRM (digital rights management) technologies to help protect copyright material, the company said today on the opening day of the CTIA Wireless 2006 conference in Las Vegas.

Microsoft provided no financial details, saying only that the investments would be "significant". It plans to extend its Windows Media Digital Rights Management software to support new types of wireless service, it said.

The company said it was responding to demands from its wireless partners, which want ways to deliver content protected by copyright. The more than 800 million mobile handsets sold worldwide each year represent a largely untapped market for digital entertainment, it said.

DRM is a catch-all term for a variety of methods used to limit content sharing. Techniques include digital encryption of songs and encoded limits on the number of times content can be accessed.

DRM has its supporters and critics. Music and film industry officials say the technology is crucial to preserving revenue in the face of piracy. But consumer advocates argue that it can be too restrictive for consumers who legitimately paid for content and want to share it on several devices.

Windows Media Digital Rights Management is licensed for use with more than 100 content services and hundreds of devices, according to the company. It protects content for delivery to PCs, mobile phones and other portable devices.