Microsoft has announced it will ship a third and final service pack update for Office 2007. It appears that Microsoft will deliver Office 2007 Service Pack 3 this month.

"The October 2011 release provides a six month window to test and deploy the release prior to exiting mainstream support," Microsoft said in a blog post Thursday.

Office 2007, which went on general sale in January 2007 alongside Windows Vista, exits what Microsoft calls "mainstream support" in April 2012. The suite will continue to be updated with security fixes for another five years after that, through April 11, 2017, during the "extended support" phase.

The biggest difference between the two support phases is that extended, non-security fixes are provided only to companies that have paid for special support contracts.

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Microsoft never issues service packs, which are mostly composed of past security and other patches, once a product is retired from mainstream support.

Office 2007 SP3 will be offered using Microsoft's now-standard procedure. Initially, the service pack will be available as a manual download and through Windows Update as an optional install. Three months later, the company will kick SP3 into Windows Update for automatic distribution and deployment.

Microsoft also usually gives corporate customers another heads-up about 30 days before it starts serving Office service packs through its update services.

Not surprisingly, Microsoft touted the newer Office 2010 as an option for customers who want to retire Office 2007 or the even-older Office 2003. Office 2003 has more than two years of life left in it: The suite won't be retired from security support until April 2014.