Using Vista Home Premium and a Belkin N type wireless system "protected" by McAfee, I often see an "intruder" on my network. All I can do is mark it as an intruder but that doesn't keep them from using my network. I know that the wireless has the WPA that supposedly only allows those with the key to connect but the intruder constantly returns. I've shut off everything in the house that might have a wireless signal and I still see the intruder. How do I completely block an intruder?