This indicates an attack attempt against a memory-corruption vulnerability in Microsoft Internet Explorer.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted CSS style object. It allows a remote attacker to execute arbitrary code.
Affected Products
Microsoft Internet Explorer 6 Microsoft Internet Explorer 7
Recommended Actions
Apply the patch supplied by the vendor: http://www.microsoft.com/technet/security/bulletin/ms09-072.mspx