Hello - Today we're releasing Security Advisory 2524375, to address nine fraudulent digital certificates issued by Comodo Group Inc, a root certificate authority. Comodo has since revoked the digital certificates. This is not a Microsoft security vulnerability; however, one of the certificates potentially affects Windows Live ID users via login.live.com. These certificates may be used to spoof content, perform phishing attacks, or perform man-in-the-middle attacks against end users. We are unaware of any active attacks.
We have taken steps to further help protect customers by developing a mitigation update. We recommend customers download the update to help protect against inadvertent use of the fraudulent digital certificates. Customers should continue to utilize Internet Explorer's Security Status bar located on the right side of the address bar to verify that the site being visited is valid and secure. The Windows Phone team is developing a mitigation update to help protect customers from the nine fraudulent digital certificates. Microsoft will provide status updates and additional guidance as soon as it becomes available.
The Microsoft mitigation will be made available through the Microsoft Download Center and the Windows Update Service. For customers who use Windows Automatic Updates, the update will occur automatically.
The video below provides additional viewpoints on the mitigation and explains why you should prioritize installation as soon as possible.
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Group Manager, Trustworthy Computing
Edited 3/25/2011 to add further information on Windows Phone