I discovered that if you place 4 unihabited spobs in a system, then place a habited spob in the system it will be shown as a vacant system unless you click on the ports list, if you place it far from the system's center and have complete radar failure it will be very hard to find as auto pilot will not help you (I think) (very good for neat missions). That way people who do not want to brodcast their location will be some what hard to find. My poast 'Invisable Spobs 101' tells how I found it and Space Pirate tod me I should poast it here.
Cheers