This indicates an attack attempt to exploit an Information Disclosure 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 Viewer
Microsoft Office for Mac 2011
Microsoft Office for Mac 2016
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.