It's likely that there's a few basic hackers in the area, and they're just hacking onto your WiFi. Using BackTrack, you can basically crack any WiFi network with a little persistence, and it's pretty unpreventable. Probably the best method would be to go into your router settings, and limit access to certain MAC addresses. While there is still a way to get around this, it's definitely a more reliable method of keeping the basic hackers off your network.