I would lean towards assuming it is a hoax.
Maybe even a friend as ironic as that sounds. Does your LSN username have part of your name in it? If you have Facebook or MySpace, the person could have found out your real name. Or if you put too much info in your profile and it was someone from your school that recognized you.
I can't believe someone would do that but I doubt they went thru all that trouble just to screw you. What is the persons name on LSN? If you were to call the schools I would just mention that you might be a victim of identity theft and tell them to ask for your SSN. I wouldn't tell them what actually happened. It would look just as bad as if the person told them.
And I agree, just make it so you can't write on your profile at all. That should take care of the person continuing to bother you.