Microsoft has released an update to help users address any exploits that can arise from the fraudulent certificates that were signed by Comodo on March 16, 2011. Actually, these could be used to spoof content, perform phishing attacks and other malicious activities. The certificates were issued to some Iranian hackers by the Certificate Authority (Comodo). For more info read this blog post. Comodo has revoked these certificates and browsers with running Online Certificate Status Protocol should be able to block these certificates. In addition, users that have enabled automatic updates are safe as well!
To read the full Security Advisory go here.