This update is one you will wish to make sure you have installed, its purpose is to block a set of Certificates that had the digital signature of Comodo as the Certification Authority on them, this could have lead to users going to an unsafe or spoofed website, which had been exploited.
Mozilla the makers of Firefox Browser have also updated Firefox to take into account of these fraudulent certificates, so do update that browser to the latest version.
Microsoft is aware of nine fraudulent digital certificates issued by Comodo, a certification authority present in the Trusted Root Certification Authorities Store on all supported versions of Microsoft Windows. Comodo advised Microsoft on March 16, 2011 that nine certificates had been signed on behalf of a third party without sufficiently validating its identity. These certificates may be used to spoof content, perform phishing attacks, or perform man-in-the-middle attacks against all Web browser users including users of Internet Explorer.
The following domains are affected by the certificates:
- login.yahoo.com (3 Certificates)
- Global Trustee
You should have already been offered this update over the last few days via Windows Update, but if you have not then run Windows Update or you can visit the download site of KB2524375 – Microsoft Security Advisory: Fraudulent Digital Certificates could allow spoofing HERE (just choose your Windows version and download and double click the file to install)
Read the full text of the advisory HERE
If you wish to double check to see if you have this update already, just open up Windows Update and click Update History, then look down the list for KB2524375, if you have it then you are ok, if not go to Windows Update or download from the link posted earlier.