Editor's Note: An earlier version of this story incorrectly identified Office 2007 as also exiting mainstream support this week.

Microsoft is shifting Windows Vista into what it calls extended support.

Vista, the problem-plagued operating system that never really took hold among users, will exit mainstream support today.

In a product's extended support phase, Microsoft continues to provide security patches to all users, but offers other fixes -- such as reliability and stability updates -- only to organizations that have signed support contracts with the company.

Just seven weeks ago, Microsoft quietly extended support for the consumer versions of Windows Vista -- as well as Windows 7 -- by five years to synchronize their support lifecycle with that of the comparable enterprise editions.

Previously, Microsoft had committed to supporting consumer software with security updates for just five years, not the 10 granted to business software.

Vista's last major update was Service Pack 2 (SP2), which debuted in May 2009.

Windows Vista's share of in-use operating systems has fallen dramatically since Microsoft introduced Windows 7 in October 2009. By the calculations of Web metrics firm Net Applications, Vista now accounts for just 7.7% of all operating systems, and 8.3% of the machines running Windows.

Vista peaked at 19.1% in October 2009 and has been falling ever since. At the rate of its decline over the last 12 months, Vista will slip under the 5% bar in January 2013.

Windows Vista will continue to run, of course: The migration into extended support does not make it inoperable. Microsoft will deliver security updates for Vista until mid-April 2017.

Users will be able to upgrade their Vista PCs to Windows 8 when it ships later this year.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is gkeizer@computerworld.com.

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