Wireless networks are a great way to share your internet service between multiple computers in your house. You can even roam the house with your laptop and still print to your printer in the study. But... is your wireless network giving your neighbors access to your personal data?
You go to the store and buy yourself a wireless router and a couple wireless adapters for your computer. The sales guy tells you how easy it is to setup and you go home and follow the instructions. Everything works great, right? Well... the problem is that unless you do a little extra work, your wireless network is wide open for the world to use. If you've got a wireless laptop, try this. Take it outside. Can you still connect to your network? What about your neighbors house? Does it work from there? Anywhere you can connect, so can anyone else. If you happen to have file sharing turned on, you are really vulnerable. The hacker kid down the street could stand in front of your house and browse your files at will.
So how do you fix it? Most wireless routers have a security feature called "Wired Equivalent Privacy" or WEP. You simply enable this on the router and provide a key much like a password. Then that key has to be entered on each computer that wants to connect to your wireless network. Most wireless routers have a web based interface for setting this up, but the details are different for each brand and model. You will have to consult your documentation or your manufacturer's web site.