Microsoft has acted to stop pirated versions of its Windows Vista operating systems being used on PCs. 

Redmond said that it had monitored a number of attempts to bypass Vista's product activation protections over the past few weeks.

"As of now there are at least two distinct workarounds that have worked to some degree, but I'm sure there are more on the way," an engineer with the username 'Alexkoc' said on the official MSDN blog. 

"One of these workarounds we have affectionately named 'frankenbuild' because it involves cobbling together files from a release-candidate build and a release-to-manufacturer build to create a hybrid that bypasses activation.

"The other workaround involves the use of some virtualisation technology and our practices for activating larger business customers."

Alexkoc said that Microsoft had been investing heavily in engineering methods to prevent pirated copies of Windows Vista being distributed and used.

"Vista will use the new Windows Update client to require only the 'frankenbuild' systems to go through a genuine validation check," he said.

"These systems will fail that check because we have blocked the release-candidate keys for systems not authorised to use them. In other words, the wrong key is being used."

Microsoft will flag the rogue software as a non-genuine copy and users will have 30 days to re-activate with a valid product key.

After that, systems will only operate in 'reduced functionality mode', which limits their use to one hour with the default web browser.

"I want to be clear that even though they can only use their browser for an hour, we will never limit their access to their data," said Alexkoc. "A user can always boot their PC into what is called Safe Mode."

Microsoft hopes that this action will help get the message out that pirating Windows Vista will have real consequences and will encourage people to check before they buy.