This site has a valid certificate.
This certificate is a statement guaranteeing the security of this Web site. A certificate contains information that a specific Web site is who it says it is. This ensures that no other site can assume the identity of the original site.
When you enter a secure Web site, Internet Explorer displays this dialog box to notify you that you are entering a secure Web site, and displays a lock icon in a locked position on the status bar. When you leave a secure Web site, Internet Explorer displays another dialog box to notify you that you are no longer on a secure Web site, and displays a lock icon in an unlocked position on the status bar.
To view the certificate for this Web site, click the underlined name in the dialog box.
If you want to see this dialog whenever you have entered a secure Web site, make sure the In the future, do not show this warning check box is cleared.