Microsoft® Office 2003 Service Pack 3 (SP3) represents a major evolution in security for Office 2003. It further hardens the Office suite against potential attacks and other security threats. This service pack also includes fixes that have been previously released as separate updates for Office 2003.
You can get specific information about this update in the Microsoft Knowledge Base article (923618): Description of Office 2003 Service Pack 3.
Source : Bink.nu
