These people are correct. Stop posting on here and call your internet provider as soon as possible. I don't know exactly what he can do or what information he could possibly steal but it's not worth finding out.
Do as these people are suggesting you do... CALL YOUR ISP! It is highly illegal and your ISP can most likely track him down and stop it from happening. Not to mention he can probably get into some trouble with the authorities.
Why do I get the feeling we my want to start watching for a bridge?