The information, posted by Charles Van Heusen, a Texas-based Microsoft technology specialist, was still available in Google's search cache today.
A company spokeswoman neither confirmed nor denied the free upgrade offer, saying only that, "Microsoft has not disclosed an Office 2010 Technology Guarantee", and declining further comment.
As first reported by Ars Technica, Microsoft will kick off the 'Microsoft Office 2010 Technology Guarantee Program' on March 5 and run the free upgrade program through September 30.
Customers who purchase an eligible copy of Office 2007 during that period will be allowed to download the corresponding edition of Office 2010 for free when the new suite launches in June.
Users who want a DVD installation disc instead will have to pay a small shipping and handling fee for the Office 2010 media.
Buyers of Office Home and Student 2007 will receive a free copy of Office Home and Student 2010, while buyers of Office Standard 2007 will be eligible for a free copy of Office Home and Business 2010, a new edition in the Office lineup. Purchases of either Office Small Business 2007 or Office Professional 2007 will be eligible for a free copy of Office Professional 2010.
Microsoft typically runs upgrade promotions in the months leading up to a major product release to sustain sales when many customers know an updated edition is due out soon.
Last summer, Microsoft used the Windows 7 Upgrade Option to maintain sales of Vista. Customers who bought a copy of the soon-to-be-replaced operating system between June 26 and October 22 were to receive free copies of Windows 7 when it launched.
As with Wednesday's Office 2010 announcement, the Windows 7 Upgrade Option leaked before it was officially unveiled.
The company also offered similar deals for free upgrades from Office 2003 to Office 2007, and from Office 2004 for Mac to Office 2008 for Mac .
Last month, Microsoft revealed prices for Office 2010, and confirmed that it would not sell less-expensive upgrade editions , as it has in the past.
Some analysts have argued that Microsoft dumped upgrades to prevent business customers from using a loophole to avoid paying Microsoft's pricey software maintenance fees.
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See also: Microsoft unveils Office 2010 RC version