This might mean that you've accessed one of our many hosted websites that live on this server, via SSL, using a web browser that doesn't support Server Name Indication
(see The Apache SNI page for more information about Server Name Indication).
If you'd like to report the problem, please email firstname.lastname@example.org telling us the exact website URL you were trying to access, what web browser you were using (which version; on which operating system), what happened exactly when you tried to access that URL, and the exact date and time it happened.
Computing Support Group
Department of Computing
Imperial College London