Very recently Microsoft released an update to resolve an issue which requires an update to the certificate revocation list on Windows Mobile devices and to keep your systems certificate list up to date. Affected systems are Windows Mobile 6.x, Microsoft Zune HD and Windows Phone 7. Remember that compromised digital certificates could allow spoofing.
The fraudulent certificates go back to the Comodo incident that happened last year and could affect login.live.com, mail.google.com, www.google.com, login.yahoo.com (3 certificates), login.skype.com, and addons.mozilla.org. Although, Comodo has revoked these certificates browsers need to have an updated version of the Online Certificate Status Protocol (OCSP) enabled to be able to block these certificates from being used.
Go here to download this update - http://www.microsoft.com/download/en/details.aspx?id=28733