But the signal that allows you to do that doesn't necessarily stop at your front door. Unless you take a few simple precautions, anyone with the right computer card can pick up your access point and surf the internet on your dime. Not only that, but they might be able to access your files while you're off doing other things.
These wireless networks, built on the 802.11b standard, also known as "Wi-Fi" and Apple Computer's "AirPort," do have a basic encryption that can offer at least some protection. Enabling this protection, as well as giving your network a unique name can slow down some hackers enough to make your network not worth their time.