It might be that person got into the database. There had to be some security leak somewhere to allow that to happen. Normal a link would not cause a problem like that. It could have allowed that person access to data that way. If it was a Vbulletin site and not patched that could be major problem as well.
Here what I got:
Service Unavailable
Guru Meditation:
XID: 427665620
Varnish cache server
