900 million Internet Explorer users hit by bug

Microsoft is investigating new public reports of a vulnerability in all supported editions of Microsoft Windows. The vulnerability could allow an attacker to cause a victim to run malicious scripts when visiting various Web sites, resulting in information disclosure. This impact is similar to server-side cross-site scripting (XSS) vulnerabilities. Microsoft is aware of published information and proof-of-concept code that attempts to exploit this vulnerability. At this time, Microsoft has not seen any indications of active exploitation of the vulnerability.
The vulnerability exists due to the way MHTML interprets MIME-formatted requests for content blocks within a document. It is possible under certain conditions for this vulnerability to allow an attacker to inject a client-side script in the response of a Web request run in the context of the victim’s Internet Explorer. The script could spoof content, disclose information, or take any action that the user could take on the affected Web site on behalf of the targeted user.