But, analysts warned, the users most likely to be directly affected are large companies that plan to install or currently are deploying either Office XP or Office 2003 bundled with the Microsoft Access database.

A U.S. District Court jury in California found last year that code primarily used in Access 2002 and 2003 infringed upon a patent held by a Guatemalan inventor.

Although Microsoft is appealing the ruling, the company last week said that it began sending e-mail notices about the upgrade requirements to corporate users of Office on Jan. 20. Microsoft said customers deploying Office 2003 with Access must install the Service Pack 2 update that it released for the application suite last September. New users of Office XP and Access are required to install a patch.

For many large companies, service pack and patch installations can be a major headache because of the extensive testing that's needed before the software can be rolled out, as well as the often lengthy deployment process itself.

Corporate users "don't want to break what's not broken." said Kevin McGrew, CEO of TechTrack Solutions Inc., an asset management consultancy in Vancouver, British Columbia. McGrew estimated that for every 1,000 PC users, an IT staff must spend a week testing new patches or service packs and then deploy them.