http://www.microsoft.com/technet/security/bulletin/ms08-078.mspx
Executive Summary
This security update resolves a publicly disclosed vulnerability. The vulnerability could allow remote code execution if a user views a specially crafted Web page using Internet Explorer. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
This security update is rated Critical for Internet Explorer 5.01, Internet Explorer 6, Internet Explorer 6 Service Pack 1, and Internet Explorer 7. For information about Internet Explorer 8 Beta 2, please see the section, Frequently Asked Questions (FAQ) Related to This Security Update. For more information, see the subsection, Affected and Non-Affected Software, in this section.
The security update addresses the vulnerability by modifying the way Internet Explorer validates data binding parameters and handles the error resulting in the exploitable condition. For more information about the vulnerability, see the Frequently Asked Questions (FAQ) subsection under the next section, Vulnerability Information.
This security update also addresses the vulnerability first described in Microsoft Security Advisory 961051.
Recommendation. Microsoft recommends that customers apply the update immediately.