Microsoft is to limit support for three versions of Vista, including the most expensive, to five years rather than 10 years.

The company defended the difference by noting that the clock just started ticking. "End of life-cycle support for Vista is still five years out," a spokesperson said.

However, the software maker left the door ajar. "As we've done in the past, Microsoft will continue to evaluate the support life cycle for Windows Vista and make decisions about extending support if and when it is necessary," the spokesperson added.

Although the corporate editions of Vista - Business and Enterprise - will be supported for the usual '5 + 5' span that includes five years of what Microsoft calls 'mainstream' support and another five of ‘extended’ support, the consumer versions currently have an end date of April 10, 2012. Vista Home Basic, Home Premium and Ultimate will stop receiving updates, even critical security updates, after that. Ultimate, which retails for £313 (£205 for an upgrade) on Amazon, is the priciest Vista edition, and is touted by Microsoft in its marketing materials as offering "all of the features found in Windows Vista Home Premium and also all of the features found in Windows Vista Business”.

Vista Business and Vista Enterprise users will receive security updates into 2017.

The decision to cut off consumer Vista support after five years seems odd in light of a January move by Microsoft that added extended support to Windows XP Home and XP Media Center. Windows XP Home and XP Media Center, which were scheduled to drop off the support chart in mid-April 2009, were given an extension to April 2014.