This indicates an attack attempt to exploit a Remote Code Execution vulnerability in Microsoft Office.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted Excel file. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted Excel file.
Microsoft Office 2003 Service Pack 3
Microsoft Office 2007 Service Pack 2
Microsoft Office 2007 Service Pack 3
Microsoft Office 2010 (32-bit editions)
Microsoft Office 2010 Service Pack 1 (32-bit editions)
Microsoft Office 2010 (64-bit editions)
Microsoft Office 2010 Service Pack 1 (64-bit editions)
Microsoft Office 2008 for Mac
Microsoft Office for Mac 2011
Microsoft Excel Viewer
Microsoft Office Compatibility Pack Service Pack 2
Microsoft Office Compatibility Pack Service Pack 3
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.