How to Detect if Someone's Stealing Your WiFi

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.

Okay, it's time to get down to it. Is your wireless network running slowly? Do you have intermittent losses in Internet access and you can't figure out why? First, take a breath. In all likelihood, no one is stealing your Internet. Tons of things could cause a slow connection. Your Internet service provider might be having issues or is overloaded with traffic. Your WiFi router might be experiencing interference from other electronics, or simply be having trouble penetrating the walls and furniture of your home to get a wireless signal to your computer.

There's only one thing you need to prevent 99.9 percent of wireless squatters from using your Internet connection: a password.

The most basic element of wireless security is an encryption protocol such as WPA2, or WiFi Protected Access. Older standards like WEP and the first generation of WPA have been phased out for the more secure WPA2. You don't need to know anything about how the encryption works -- you just need to set up WPA2 security on you wireless router and set a password for the network. Make it something you can remember that's not easy for others to guess (please don't use "password" or "12345!") and you'll be well on your way to security.

So how do you do all of that? Well, that varies by the type of router you have, but most WiFi routers are accessible from a connected device via the address http://192.168.1.1 in a Web browser. Logging in is usually easy, too, as most router manufacturers use a simple pair of words like "root" and "admin" for the device's login and password (you should be able to find this information in the manual). That will take you to a management tool where you can change all kinds of settings, including your wireless security.

That tip might set off a little security alert in the back of your head. "Wait, a minute," you think. "If most routers use the same local address and login/password, couldn't anyone get in there and mess with my security settings?" Well ... yes! Without a password, your wireless network is open for anyone to hop on. But a password isn't quite all you need to be totally secure. You should also change the router's login information to something aside from the usual "admin." That will keep virtually everyone from messing with your router -- but let's take a look at how to detect a WiFi leach, just in case.

Mac users can go through the Airport utility to see a list of connected users.

Screen capture by HowStuffWorks staff

With WPA2 security enabled, it's unlikely anyone will ever piggyback on your network. But there's an easy way to spot squatters: Since every device connected to your network has a unique IP address and MAC address, you can easily see a list of connected devices -- often listed as "clients" -- on one of the settings pages for your wireless router. Many devices broadcast an ID because they've been named by their owners, so if you see "John's Laptop" connected to your network and you don't have a John in the house, you've found trouble! Even if a device doesn't show a name in the router's client list, you can count the number of devices connected and compare to the number of devices you know should be there to see if the numbers are off.

Want to make absolutely sure no one's going to figure out your password and worm their way onto your network? You have a few options. Your router can hide its SSID, meaning it won't show up for anyone searching for connectable networks. The address will have to be entered manually. You can also set up a wireless MAC filter to "whitelist" devices you own, disabling access for anyone else. Of course, this makes it a bit tougher for welcome guests, such as friends, to get online at your house.

Internet monitoring software is also an option. For example, free utility AirSnare will alert you when unfamiliar MAC addresses log onto your network. But with a secure connection, you shouldn't have to worry about that. The truth is, WiFi is not a precious commodity like it once was. You can get it at practically any coffee shop. Millions of us carry around smartphones with always-on data connections. To some degree, that makes WiFi access a faster, cheaper option of Internet access, but it's not always the most convenient one.

As long as your network is passworded, only a hacker using specialized software is going to get past your security. Technology site Ars Technica has detailed how a $2500 program called Silica can be used in conjunction with Web sites containing dictionaries of millions of words to connect to a secured network and crack its password [source: Ars Technica]. But there's still an easy way to stop even serious hackers in their tracks: Use a better password. The longer and harder to guess, the safer your network will be.

With a strong password, you shouldn't ever have to worry about keeping tabs on who connects to your network. Piggybackers will have to find someone else to mooch off of.

Originally Published: Apr 30, 2009

Author's Note

Smartphones changed everything, didn't they? A few short years ago, we hoarded WiFi like a precious commodity. Your neighbors might steal it! Criminals might park outside your house and download illegal files on your network! Sounds horrifying, doesn't it? Well, once we got smartphones with omnipresent data connections, we calmed down a bit. WiFi is now so ubiquitous that you don't have to worry too much about you neighbors leeching off of you -- they've probably got WiFi, too. We don't need to find hotspots when we've got 3G and 4G on our phones. Updating this article, it was amazing to see how much our Internet access has changed in a few short years. And wireless security is a lot better, too -- the article's old mentions of WEP felt archaic in a much more secure WPA2 world. In a few years, someone will no doubt look back on my update revision and say "WPA2? How quaint!"

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