How to check if someone is using your WiFi

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Matthew M. White
@matthewmwhite
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Having a network to administer was once a job for IT specialists in large companies. However, the world has become more technologically advanced, so now businesses large and small, most households and libraries have their own network to manage and maintain. These days, setting up a WiFi connection is simple and inexpensive.

Some users have a WiFi network running from their cable or DSL Internet service, while others use WiFi using their smartphone as an access point. Most smart phones have the ability to act as mobile hotspots and tether a wireless Internet connection to other devices.



Signs someone is accessing your WiFi

No matter how many of us currently use WiFi, most of us haven't been trained in network security. This means that your WiFi network may very well be vulnerable to malicious hackers or those who simply want to use your Internet access for free, anyway it is unwanted and illegal.

It helps to be aware of some warning signs that may indicate someone is connecting to your network without permission. A common sign is a slower internet connection. Every Internet connection consumes bandwidth, and if someone downloads torrents or plays online games on your network without your permission, your traffic will slow down.

Knowing who is using your WiFi and when is crucial to keeping your network secure. This tutorial will show you how to check if someone is using your WiFi, how to turn it off, and how to prevent them and anyone else from accessing your WiFi again.


Check who is using your WiFi network

There are several ways to detect whether someone is using your wireless network or not, let's look at some of them.


Simple methods to check if someone is accessing your WiFi

A simple way is to turn off all your computers, smartphones and tablets so that none of your devices are on. Next, check the activity lights on your wireless router (often referred to as a wireless modem if you're connected to high-speed cable or DSL Internet). If regular activity still appears on the router even though none of the authorized users are on, it's a sign that someone is using your WiFi without your permission.

Using the Web Browser to Access Your Router

The next step is to use a web browser to connect to your wireless router's access page. Almost all home routers have an online access page that you can access from any computer that is linked to the router.

Common URLs for Routers

The URL to type into your browser window varies from router to router, but it is almost always an IP address. You can find the exact URL by consulting your router's documentation. Check on the router itself if the address is printed on the label, or by using the default addresses: a lot of routers use http://192.168.0.1 or http://192.168.1.1.

If you use Xfinity (Comcast) to access the Internet, the default URL to access your router/modem may be http://10.0.0.1/.

You can simply enter the number (for example, "192.168.0.1") into your browser's address bar and press enter. This will take you to your router's administrative interface. You can find information about Netgear Routers here, Belkin Routers here, and information about Asus Routers here.



Router Login Credentials

You will need to know your router's administrator password to log in. You must have saved this password when you set up your router, or it must have been set for you by the installation technician if you had someone else set up your network. .

The most common default username is admin and the most common default password is admin as well. Other very common default passwords are "1234" or just the word "password".

If you're using a router/modem that came with your Comcast/Xfinity service and you haven't changed the password from the original, the default username might be admin and the default password maybe just password.

Identification of connected devices

Once connected, take a look at your router's administration page for the list of connected devices. On a Netgear router this is usually listed under Maintenance>Connected Peripherals. On a Linksys Router, it is listed under Network Map.

Other routers will have their own organizational structure for this information, but each router should provide it. Once you're listed, you can identify each device listed by its MAC address.

Here is a TechJunkie article offering a quick explanation of MAC addresses sums. All you need to know for now is that each device has its own unique number which is used to identify it on the local network, which is your WiFi network in this case.

You can find the MAC address of all your computers, compare them to the list, then see if there are any devices on the list that you don't recognize as belonging to an authorized network user.



If you're having trouble identifying all the devices listed, turn off your devices or refresh the map. It is a process of elimination. Don't forget to include smart TVs and any other devices connected to your WiFi such as Roku players or Amazon Echos.

If all that messing around with the MAC address and router management pages is a little out of your technical comfort zone, don't worry. There are some great third-party tools out there that will help you get the job done.

F-Secure Router Checker

One such great tool is the F-Secure Router Checker. It is a free and quick solution to see if your router has been hacked or not.

Simply go to the website, select the blue "Check your router" button and let the website do its thing. It will assess all vulnerabilities in your router and notify you.

The WiFi Inspector

Another route is to download WiFi Inspector, a Google Play app that scans your WiFi network and tells you which devices are using it. This is a good way to identify devices accessing your network.

ZMap

A simple and great tool to use to analyze a WiFi network is ZMap. Although it currently only works on MacOS, Linux, and BSD, ZMap is an easy-to-use tool that provides plenty of features and a graphical interface to make it simple to understand. Windows users don't worry, you can easily run ZMap in a virtual machine.

Often touted as the teacher of NMap, ZMap is a program you want to have in your virtual tool belt.

Secure your WiFi network against intruders

What to do if you identify someone who is using your WiFi network without your permission? The first step is to delete them, then make sure they can't do it again.

The instructions below are tested using a Linksys Smart Router. Your router may differ slightly and use different terminology. Simply adapt the following instructions to your specific model.

  1. Log in to your router and access the administration interface.
  2. Select the wireless part of the interface or search for the guest network.
  3. Disable the Guest network unless you specifically use it.
  4. Disable wireless. On a Linksys router, this is a toggle. This will knock everyone off your WiFi, so let everyone know ahead of time.
  5. Select WPA2 as the wireless security mode if it is not already selected. This is the best option for most users.
  6. Change the wireless access password and save the changes.
  7. Enable wireless again.
  8. Change the password on all devices that connect to WiFi.

If your router does not support WPA2, you must upgrade; it is the de facto standard for wireless security. To learn more about choosing the right router, please see this TechJunkie article on how to buy the right router for your needs.

Change the password to something as difficult as possible while still being able to remember it. Mix upper and lower case letters and numbers. If your router allows it, add a special character or two for good measure.

Additional Wi-Fi Security Measures

Additional steps you can take include disabling WiFi Protected Setup and upgrading the router firmware. There should be a setting in the wireless part of your router that disables WPS. This is a known vulnerability in shared properties, dorms, or other places where you don't control who comes and goes. Disable it to prevent people from authenticating to your network if they have physical access to the router hardware.

Upgrading router firmware allows your router to benefit from any patches or security patches. The recent KRACK vulnerability is a good example of this, it found a weakness in WPA2 which was quickly fixed. Only a router firmware update can fully protect you, so allow automatic updates on your router if possible, otherwise check for updates regularly.

These are the basics to check if someone is using your WiFi and how to prevent them from doing so again. Do you know of any other ways to achieve this goal? If so, share them with us in the comments below!

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