More specifically, the message is:
You have asked to be warned about certificates from 'GTE CyberTrust Global Root'
Click on Preferences under the Tools menu (or press CTRL+F12).
Select the Advanced tab. In the left pane, select Security.
Click the Manage Certificates button.
Click the Authorities tab. Scroll down to "GTE CyberTrust Global Root" and select it.
Click the View button.
Ensure the checkbox labeled "Warn me before using this certificate" is unchecked.