Quoted from an MSDN document:
A recent decision from a court case has determined that certain portions of code found in Microsoft Office Professional Edition 2003, Microsoft Office Access 2003, Microsoft Office XP Professional and Microsoft Office Access 2002 infringe a third-party patent. As a result, Microsoft must make available a revised version of these products with the allegedly infringing code replaced.
To comply with the court order Microsoft is now requiring all future deployments of Microsoft Office Professional 2003 and Microsoft Access 2003 to include service pack 2. Microsoft is also requiring all new deployments of Microsoft Office XP Professional and Access 2002 to include a special patch.
Customers who have previously installed affected products are being requested to voluntarily install the patch although installation is not required. In order to ensure customers are aware of these new requirements, Microsoft has been mailing notification letters throughout the month of January.
We have received requests from customers to provide more information about the situation leading to this requirement. The attached frequently asked questions document goes into more detail on the circumstances related to this requirement, information on deployment and additional context to the legal situation.
Use caution when installing this patch, if you do at all. It has a tendency to break Office programs and cause inexplicable crashing. If you have a bootleg copy of the software, I definitely wouldn’t recommend installing the update. Just a heads-up.