The move is highly unusual. In the past, Microsoft has terminated downgrade rights -- which let customers replace a newer version of Windows with an older edition without paying for two copies -- within months of introducing a new OS.
While few consumers may want to downgrade from Windows 7 to XP -- unlike when many mutinied against Vista three years ago -- businesses often want to standardize on a single operating system to simplify machine management.
Monday's announcement was the second Windows XP downgrade rights extension. Microsoft originally limited Windows 7-to-Windows XP downgrades to six months after Windows 7's release, but backtracked in June 2009 after an analyst with Gartner Research called the plan a "real mess."
Instead, Microsoft later said it would allow downgrades to Windows XP until 18 months after the October 2009 debut of Windows 7 , or until it released Windows 7 SP1.
In either scenario, XP downgrade rights would have expired sometime in 2011, perhaps as early as April.
On Monday, Microsoft again changed its mind. Users running Windows 7 Professional or Ultimate will now be able to downgrade to Windows XP Professional throughout the entire lifecycle of Windows 7.
"Our business customers have told us that the removing end-user downgrade rights to Windows XP Professional could be confusing," said Microsoft spokesman Brandon LeBlanc, in an entry on the a company blog .
Windows 7 Professional won't be fully retired until January 2020; the Ultimate edition will be put out to pasture five years earlier, in January 2015.
How to keep Windows XP SP2 safer after Microsoft stops patching
Maybe you didn't get the memo: Tomorrow marks the end of patches for Windows XP Service Pack 2 (SP2).
And you're still running the nearly-six-year-old edition.
But XP SP2 won't shudder to a stop. Although Tuesday marks the support retirement of the service pack -- a date that some have called a "red alert" for people running SP2 -- that doesn't mean your copy of Windows will suddenly refuse to run.
It does mean that, after tomorrow, Microsoft will not offer any security patches, no matter how severe the vulnerability, no matter what part of Windows or associated component is involved. No more Windows patches -- and no more patches for Internet Explorer (IE), no patches for Windows Media Player, no patches for Outlook Express.
You can, of course, sidestep the whole problem by upgrading to Windows XP SP3, which will be supported until April 2014: Microsoft has posted a page that explains how to do that here. (Note: Because there is no SP3 for the 64-bit version of Windows XP, you'll continue to receive security updates if you're running SP2 of that edition.)
Among your options: Download and install SP3 via Windows Update, download a disk image for upgrading multiple machines or order a SP3 CD for $3.99.
In fact, you actually have four weeks to upgrade to SP3 before Microsoft releases the next likely XP patch on Aug. 10. There's little chance that Microsoft will issue an "out-of-band" emergency update before then.
But if you're committed to SP2, for whatever reason, and have no intention of upgrading anytime soon, there are steps you can take to make your PC more secure and your time on the Internet safer.
Dump Internet Explorer. After Tuesday, Microsoft won't be providing IE patches of any kind, for any version -- IE6, IE7 or even 2009's IE8 -- to people running Windows XP SP2.
But other browser makers aren't halting updates for their wares. Mozilla, Google, Apple and Opera will be shipping fixes for Windows XP versions of their Firefox, Chrome, Safari and Opera browsers for the foreseeable future.
More than a year ago, Mozilla debated whether to drop support for older editions of Windows, including Windows 2000 and Windows XP SP2. But the company decided against the move.
According to the system requirements for Firefox 4 Beta 1, the preview Mozilla released last week, the browser runs not only on Windows XP, but also Windows 2000. (Mozilla's systems requirement link for Firefox 4 currently takes you to the page for version 3.6.6, leading us to believe that the requirements will remain the same for Firefox 4, which is slated to ship in November 2010.)
And because Mozilla's policy is to continue supporting a browser with security updates for at least six months after the launch of its successor, moving to Firefox 4 down the road means that if the company ships Firefox 5, or whatever the next edition is called, a year later -- in November 2011 -- patches for it will be produced through May 2012 or later.
It's important to keep a browser up-to-date on patches because hackers continue to exploit browser vulnerabilities, particularly those in IE. They focus on IE bugs for a simple reason: Every Windows machine has it, and Microsoft's browser continues to be used by more people than any other.
Ironically, you may actual improve the security of your Windows XP SP2 machine if you dump IE.
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