Office Genuine Advantage (OGA) is a similar tool as Windows Genuine Advantage (WGA) from Microsoft that checks and validates via an online validation process to verify that the copy of Microsoft Office System productivity suite or their individual applications installed on your system is genuine, licensed and legal. Previously, genuine Office validation process is voluntary, but as of October 2006, the Office Genuine Advantage validation test is mandatory.

Microsoft will require Office XP, Office 2002, Office 2003, Office 2007 System or later version of Office suites or individual applications of Office such as Word or Excel to be validated when users want to download Office Online templates and other add-ons or updates from within Microsoft Office System 2007 applications, or when want to access downloads from the Microsoft Download Center that are reserved for genuine users and other special offers.

By January 2007, Office customers must also complete the OGA authentication test to use Office Update to download updates.

Users who unknowingly acquired counterfeit or pirated versions of Microsoft Office System should contact Microsoft to check if they qualified to receive a complimentary copy of Microsoft Office.

Update: Office Genuine Advantage Notifications (KB949810)