&gt; <i>Why?</i><p>Your not limited to a single response.  You could turn the URL red for a week and then after that do a popup etc.  hell you could stup a browser to ignore expiration dates with minimal impact.<p>Remember, certificates are not some binary entity.  You can have high and low trust certificates ex: trust to sign OS code, trust to sign user land code etc.<p>Your stuck in binary terms which are useless from a security standpoint.