This indicates an attack attempt to exploit a Code Execution vulnerability in Microsoft Excel.
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 2007
Microsoft Office 2010
Microsoft Office 2013
Microsoft Office for Mac
Microsoft SharePoint Server 2013
Microsoft Excel Viewer 2007 Service Pack 3
Microsoft Office Compatibility Pack Service Pack 3
Microsoft Word Viewer
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.