Hi all,
I usually get certification error message when I try to access CentOS website. The below is what I got in firefox this time. What's the issue? CentOS is one of the respected distros. How should I take this?

Secure Connection Failed

www.centos.org uses an invalid security certificate.

The certificate is not trusted because the issuer certificate is not trusted.
(Error code: sec_error_untrusted_issuer)

    * This could be a problem with the server's configuration, or it could be someone trying to impersonate the server.
    * If you have connected to this server successfully in the past, the error may be temporary, and you can try again later.