By Joe Stoddard. If you happen to be driving around and see funny marks on the sidewalk, it might be kids playing hopscotch, it might be the utility company marking out gas lines, or it could be "War-Chalking"--the latest method hackers are using to identify an accessible wireless network. The term derives from "War Dialing"--using a predictive dialer to hack into modems, and "War Driving"--cruising the neighborhood with a WiFi-equipped laptop hoping to get online for free by borrowing a little of your bandwidth.

If you're a small builder with a wireless network in your office, you're at risk. The solution: change the default ID and password settings of your router. You can also use wireless encryption, and filter users by their IP or MAC (hardware) address.