An anti-piracy feature in Windows Vista is to be removed by Microsoft following consumer complaints.

The so-called " kill switch" was designed to prevent users with illegal copies of Vista or people who do not validate genuine copies from using certain features. But users claimed that glitches meant some legal copies of Vista had been disabled.

Currently, if Vista users do not activate their operating system within 30 days, or three days after a major hardware configuration change, (which means Windows Vista determines that it is running on a different computer or is a counterfeit copy), or if an activated system fails a validation check, the built-in feature imposes tough restrictions.

There is either a “non-genuine reduced functionality mode” or the more restrictive "out of grace reduced functionality mode”. Users will, however, continue to have access to their files via safe mode.

With the out of grace mode, the time a person can remain logged onto their PC with Vista is limited to one hour, and they have access only to their browser and options for resolving their system’s non-genuine status; in addition, their data is preserved but they are denied access to all other features of Vista.

The non-genuine mode restricts access to premium content from the Microsoft Download Center. Both modes restrict premium features such as Aero Glass, and Readyboost from working.

The aim of "kill switch" was to clamp down on pirate copies of Vista, which Microsoft say are down. It said efforts to tackle piracy had seen numbers of fake copies of Vista at half the level of XP, the previous Windows operating system.

So instead of disabling non verified or fake copies, Microsoft will revert to its Windows Genuine Advantage (WGA) program. This online authenticity verification system introduced in 2006 checks that the user's version of Windows is genuine. For XP users it was a voluntary option but became mandatory for Vista users.

All copies of Vista will still require activation and the system will continue to validate from time to time to verify that systems are activated properly. But while users of non-genuine versions will have access to all Vista features, they will have to tolerate constant nagging messages and screens telling users they are using counterfeit copies; the notifications will include a link to buy a genuine copy.

However, Microsoft said it plans to close a loophole that lets pirates mimic activation and will also clamp down on a loophole used to extend the "grace period" time between installation and activation.

The changes come into force with Windows Vista Service Pack 1, the first major update to the operating system, which is expected in the first quarter of next year.