This indicates an attack attempt against a remote code-execution vulnerability in Microsoft Excel.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted Excel file. It allows a remote attacker to execute arbitrary code.
Affected Products
Microsoft Office Excel 2003 SP2 Microsoft Office Excel Viewer 2003 Microsoft Office Excel 2002 Microsoft Office Excel 2000 Microsoft Excel 2004 for Mac
Recommended Actions
Apply the patch available at the vendor's web site: http://www.microsoft.com/technet/security/bulletin/ms08-014.mspx