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 Excel 2000 Service Pack 3 Microsoft Excel 2002 Service Pack 3 Microsoft Excel 2003 Service Pack 2 Microsoft Excel 2007
Recommended Actions
Apply the patch available at the vendor's web site: http://www.microsoft.com/technet/security/bulletin/MS08-014.mspx