This indicates an attack attempt towards a memory-corruption vulnerability in Microsoft Internet Explorer.
The vulnerability is caused by the software's inability to properly handle attempts to access an object that has been deleted. An attacker may exploit this to cause denial of service or remote code execution.
Internet Explorer 5.01
Internet Explorer 6
Internet Explorer 7
Internet Explorer 8
System Compromise: Remote attackers can gain control of vulnerable systems.
Please refer to the following web site for the latest update or patch: