This indicates an attempt to exploit a function pointer override vulnerability in Microsoft Excel products, which is due to insufficient validation of an index value in the NAME record.
Microsoft Office 2000 Service Pack 3
Microsoft Office XP Service Pack 3
Microsoft Office 2003 Service Pack 3
2007 Microsoft Office System and its Service Pack 1
Microsoft Office Excel Viewer 2003 and its Service Pack 3
Microsoft Office Excel Viewer
Microsoft Office for Mac
Microsoft Office 2004 for Mac
Microsoft Office 2008 for Mac
Open XML File Format Converter for Mac
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the patch, available from the vendor's web site: