This indicates an attempt to exploit a memory corruption vulnerability in Microsoft Excel.
The vulnerability may allow user assisted remote attackers to execute arbitrary code via a crafted Excel file with an incorrect BIFF version value.
Microsoft Excel 2000 SP3
Microsoft Excel 2002 SP3
Microsoft Excel 2003 SP2
Microsoft Excel 2003 Viewer
Microsoft Office Excel 2007
System compromise: privilege escalation, remote code execution.
Microsoft has released a fixes to address this issue.