The Vista system will be available to consumers at the end of the month. However, in an interview with The Times, one of its chief architects said that because of anti-piracy protection granted to the Hollywood studios, Vista would not play HD-DVD and Blu-ray Discs on certain PCs.

Dave Marsh, the lead program manager for video at Microsoft, said that if the PC used a digital connection to link with the monitor or television, then it would require the highest level of content protection, known as HDCP, to play the discs. If it did not have such protection, Vista would shut down the signal, he said.

The admission will be a blow to Microsoft, which is hoping that more users will turn to their PCs for watching films and other content.

According to DSG International, which owns PC World, about 15 per cent of PCs sold at present in Britain use digital connections, but that number is expected to grow.

Virtually none of the PCs that use a digital connection have HDCP. “It’s up to the content providers to set the level of protection that Vista applies, but they’re likely to be pretty firm on the need to use high-definition content protection [HDCP] when using a digital connection,” Mr Marsh said. “At the moment HD DVD and Blu-ray Discs certainly require such protection.”

Mr Marsh added that computers with built-in HDCP protection — which could play such discs — were being phased in, but that, in the meantime, Microsoft was obliged to ensure that the studios’ content was being used securely.

Computers using an analog connection will not be affected and the requirement does not apply to regular DVDs.

Peter Gutman, a researcher in computer security at the University of Auckland, who produced a report on the compatability of Vista with various hardware, said: “When this aired at a couple of Windows conferences last year, I thought: ‘This is so bad it’s going to die.’ But it didn’t.

“To downgrade the signal so that the HD-DVD will play, you need a constrictor, but that doesn’t seem to be present in many of the computers that are shipping. Given that it downgrades signal quality, most manufacturers aren’t rushing to include it.

“Any computer which has an LCD monitor is potentially at risk of not being able to play this content.”

A DSG International official said that the number of PCs with digital connections would grow as the computer came to be used more as an entertainment device.

“The PC is moving out of the study and into the living room as users begin to connect up their computers with their TV,” the official said. “The majority of HD-TVs sold now have a digital input on the back.”

Protection still full of holes

Explore Tech & Web News

• Personal Tech

• The Web

• Gadgets & Gaming

Times recommends

• Billion-pixel panoramas — from your own camera
• One gadget to rule them all
• The future of social networking: mobile phones