This indicates detection of an attempt to exploit a remote code execution vulnerability in Microsoft Internet Explorer.
The vulnerability is a result of the way that Internet Explorer accesses an object that has not been correctly initialized or that has been deleted. A reference counting bug in MSHTML.DLL can be exploited to allow code of an attacker's choice to run in the context of the currently logged in user.
Microsoft Internet Explorer 6
Microsoft Internet Explorer 7
Microsoft has issued an update to correct this vulnerability. More details can be found at: