There is an unknown computer showing up in the sidebar of my MacBook (running 10.5.5) under "shared." It's called "mac02354a......" It shows up under my the iMac which I am posting this with. It says I am connected as a guest, but don't know what it is or where it came from. If I right-click on it under Get Info it says PC Server. I don't own a PC. Another strange thing is, its not showing up on my iMac. How do I disconnect, or get rid of it? Should I be worried? THanks.