If it is finding and displaying your friends, mates, computer name then it is on your network (LAN, Local Area Network).
Is your Mate in the same dorm room as you? In the same building as you? Going to the same school as you?
All computer today are set to look for other computer connected to the same LAN (Network).
When you put the cursor over the Shared label you should see a popup to the right of it that says Hide. Click that.
First it's not a dilemma. Having that there mean nothing other then both of you are on the same LAN and the computers list in that area have Sharing enabled. Even if you don't have sharing enabled other computer that do and are on th same LAN will show up in that area. Noraml and nothing wrong with it. As I said above Hide the Shared section.
I fail to understand why you are so concerned about this. If this is your friend. He can not connect to your computer if he does not know your password.