Before you can detect if someone is ripping off your wireless Internet connection, it's important to understand some basic computer networking lingo. For more information on how to set up a wireless network, take a look at How WiFi Works. Now, let's look at a few of the areas in a wireless network that will give you a baseline for determining if your WiFi signal is being sapped unexpectedly.
A wireless network is comprised of a broadband Internet connection from a DSL, cable or satellite modem. You attach the modem to the wireless router, which distributes the signal and creates a network.
This is what's called a local area network (LAN). This LAN is where you set up computer peripherals such as your desktop or laptop computer and printer. Your router will have what's called a dynamic host client protocol (DHCP) table. In essence, your DHCP table is your guest list of every allowed piece of computing equipment.
Each device has its own media access control(MAC) address. Think of this as its signature. Your router uses these addresses to assign each machine on your network an Internet protocol (IP) address. The MAC and IP addresses of your equipment will be useful in a moment when we look at ways to detect whether or not someone is stealing your WiFi. For a more in-depth understanding of IP addresses, read What is an IP address?
There are also a couple of important terms related to WiFi that you should know. A service set identifier (SSID) is the name that identifies a wireless network. By default, this will probably be the name of your router -- Netgear or ASUS or something similar -- but you can have fun by changing it to something more personal or creative, like Abraham Linksys. Today's most commonly used WiFi speed, 802.11n, is capable of up to 600 megabit per second data transfers. 802.11ac is the next standard, which will allow for wireless speeds of over one gigabit per second. 2.4GHz and 5GHz are two different wireless frequencies used in wireless routers.
If you're confused by some of this computer rhetoric, don't be. What's important is that you know what to look for when we get ready to diagnose your WiFi connection. Speaking of which, let's get to it in the next section. After all, that's what you came here for.