This indicates an attack attempt against a remote code-execution vulnerability in Microsoft Office.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted Office file. It allows a remote attacker to execute arbitrary code.
Microsoft Office XP Service Pack 3
Microsoft Office for Mac
Microsoft Office 2004 for Mac
Microsoft Office 2008 for Mac
Microsoft Office for Mac 2011
Open XML File Format Converter for Mac
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the patch supplied by the vendor: