Read the following scenario:
Jack was traveling for his job. The internet card provided by his company was not working and he had an important project due that day. James was in a small town about an hour away from the nearest internet kiosk, so he decided to drive around a nearby suburb to see if he could find a wireless system he could "borrow" to send out his project. James found a wireless system without a security key and, after parking near the home
with the system, uploaded the project. Afterward, just for fun, James peaked into the computer on the wireless system and found, to his dismay, some bank accounts and passwords.
Think about how you would feel if Jack were parked outside your home, using your wireless network.