This indicates an attack attempt to exploit a Memory Corruption vulnerability in Microsoft Internet Explorer.
The vulnerability is due to an error when the vulnerable software attempts to access an object that has been freed. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application.
Microsoft Internet Explorer 8
Microsoft Internet Explorer 9
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.