Possible hacking of Root in single user mode

I am a student at the school. Trusted with the Admin pass. There was a incident today with a kid booting into single user mode then somehow setting the computer to boot like from a mac os x cd. When there is no cd in there. When it boots it lists the laungiges. I clicked english and then it played the famous music with Welsome in every tounge. HOW DID HE DO THIS??? This is a major issue. I have never heard about this. I figure he did it from root in single user mode. He got into root via something like the link below. See number 3. Please help. We need to prevent this from happening again.


http://www.spy-hill.com/~myers/help/apple/EnableRoot.html



Thanks

 

Thank you.