This indicates an attack attempt against a Memory Corruption vulnerability in Microsoft Internet Explorer.
The memory corruption occurs when the application attempts to access uninitialized memory in certain situations. This could lead to a crash of Internet Explorer or to remote code execution.
Internet Explorer 5.01 Service Pack 4 when installed on Microsoft Windows 2000 Service Pack 4
Internet Explorer 6
Internet Explorer 7
Please refer to the following web page for an update and more detailed information: