It's really weird when several neighbors all unknowningly have unsecured wireless overlapping each other. The people in one house may be using their neighbor's wireless internet thinking that they were in fact using their own. I was in a house once where the homeowner was telling me that he was in the process of moving his wireless box to another room so it was temporarily disconnected. He said that he was surprised his internet was still working fine and assumed that the wireless box did not have to be plugged in to work. Of course it doesn't have to be plugged in if you are stealing your neighbor's wireless connection!
You've heard about those new wireless video cams. Some people install them all over the house so from many miles away they can keep an eye on the baby's room, the pets, the garden, the entry doors. If someone can get access to your wireless network, it becomes all the easier for them to access your cameras and see whats going on in your own home. This could go on for months and you may never know it.
The solution is to secure your wireless system as soon as you install it in your home. The wireless box has 1 or 2 little antennas on it and its called a wireless access point or sometimes a wireless router. Making it secure is not difficult, but you need to follow the step-by-step instructions that came with the unit. Most people only do step one which is to plug the unit in. If you keep reading, you'll see a section that describes how to set up a secure password. Look for the initials WEP or Data Encryption and that should be checked on. You'll have to store a password for each wireless computer in your home. Its not hard to do and you'll have less reasons to worry about strangers having access to your home network.