I have my own internet supplied by the cable company, but when I plug in my wireless reciever, I'm able to access an unsecured network. I figure it's either the upstairs tenents or someone else close by. 1. Is it illegal to use this "free" internet? 2. Will the party using this network be able to tell in any way that it is me that is leaching from it? 3. Could they experience performance decreases from me using the network?