This indicates an attack attempt to exploit a Memory Corruption vulnerability in Microsoft Office.
The vulnerability is due to improper handling of objects when the vulnerable software attempts to access a specially crafted excel format file. An attacker can exploit this to execute arbitrary code within the context of the logged in user via a crafted excel format file.
Microsoft Excel 2007 Service Pack 3
Microsoft Office Compatibility Pack Service Pack 3
Microsoft Excel Viewer
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.