This policy setting specifies whether to automatically update root certificates using the Windows Update website.
Typically, a certificate is used when you use a secure website or when you send and receive secure email. Anyone can issue certificates, but to have transactions that are as secure as possible, certificates must be issued by a trusted certificate authority (CA). Microsoft has included a list in Windows XP and other products of companies and organizations that it considers trusted authorities.
If you enable this policy setting, when you are presented with a certificate issued by an untrusted root authority, your computer will not contact the Windows Update website to see if Microsoft has added the CA to its list of trusted authorities.
If you disable or do not configure this policy setting, your computer will contact the Windows Update website.