If a stranger successfully gets onto your WiFi network, they may be stealing more than bandwidth. After all, they have access to your computers. Your home network should be more secure than the café's down the street.

The first thing you need to do is make sure that no one can get into that network easily. That means setting up your router to use WPA, or better, WPA-2 security.

Because I don't know what kind of router you have, I can't tell you exactly how to do that. Check your router's documentation. Generally, you enter a particular IP address into a browser, which will take you to an HTML-based configuration program located inside the router's firmware.

Setting up security will require you to create a password. Make it a that no one will be able to guess. But remember that you'll have to enter that password into every computer, smartphone, Blu-ray player, or other Wi-Fi-equipped device in your home, including overnight guests' laptops. (HDTVs and Blu-ray players are the worst for entering passwords--remote controls just aren't friendly for text entry.)

Okay, I've told you how to control who gets access, but I didn't actually answer your question: How do you see if someone is on your network who shouldn't be?