This indicates detection of an attempt to exploit a heap base vulnerability in Microsoft Outlook Express versions 5.5 and 6.
The vulnerability may allow a remote attacker to execute arbitrary code with the privileges of the victim via a Windows Address Book (.wab) file with a malformed "Property Size" field of objects with Unicode and octet string types stored in the "User Property" section.
Microsoft Corporation: Microsoft Outlook Express 5.5 SP2
Microsoft Corporation: Microsoft Outlook Express 6.0
Microsoft Corporation: Microsoft Outlook Express 6.0 SP1
System Compromise: Remote code execution.
Apply the appropriate patch for your system.