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How To Check if Someone is Using Your WiFi

Posted by Robert Hayes on March 5, 2019

It used to be that having a network to administer was a job for specialists in big companies. Then networking became more and more popular and even small businesses had their own network, usually a wired one using CAT5 Ethernet cable. But these days, wireless networks (WiFi) have become so inexpensive and easy to set up that just about every household has one. Some people have a WiFi network running off their cable or DSL Internet service, while others run WiFi using their smartphone as an access point. Regardless of the how, a lot of people have WiFi networks now, but most of us haven’t been trained in network security. That means your WiFi network may well be vulnerable to being hijacked by another user.

Internet access is relatively inexpensive, but some people just want it for free, while others have more nefarious purposes in mind. There are some warning signs that might indicate that someone is taking advantage of your network without your permission. One common sign is that your WiFi network seems to be slower than usual. Every Internet connection takes up some bandwidth, and if someone is downloading torrents or playing online games on your network without your permission, then your traffic is going to slow down somewhat. Another telltale sign is the receipt of a copyright infringement letter from your ISP saying that you’ve been caught downloading copyrighted material, when you know that you haven’t done anything of the sort. Either of those can be a sign that your wireless network has been compromised.

Knowing who is using your WiFi and when is crucial for keeping your network secure. This tutorial will show you how you can check if someone is using your WiFi, how to kick them off and how to stop it happening again.

Check who is using your WiFi network

There are several ways to detect whether or not someone is using your wireless network. One low-tech way is to shut off all your computers and smartphones and tablets so that none of your devices are turned on. Then check the activity lights on your wireless router. If there is still regular activity on the router even though none of the authorized users are powered on, then that’s a sure sign that someone is playing shenanigans.

The next step is to use a web browser to log onto your wireless router’s access page. Nearly all home routers have an online access page that you can get to from any computer that is linked to the router. The URL to type into your browser window varies from router to router. You can find the exact URL by checking your router documentation, looking on the router itself to see if the address is printed on the label, or by using the default addresses: a huge number of routers use 192.168.0.1 or 192.168.1.1. Just type the number (i.e., “192.168.0.1”) in the address bar of your browser and hit return. (You can find information on Netgear routers here, Belkin routers here, or Asus routers here.)

You’ll need to know the administrator password for your router to log on. You should have recorded this password when you set up your router, or it should have been set for you by the installation technician if you had someone else do your network setup.

Once you’ve logged on, you can look on your router’s administration page for the list of connected devices. On a Netgear router, this is usually listed under Maintenance->Attached Devices. On a Linksys router, it’s listed under Network Map. Other routers will have their own organizational structure for this information, but every router should provide it. Once you are at the list, you can identify every device listed by its MAC address. (Here’s a quick explanation of what MAC addresses are; all you need to know for now is that every device has its own number.) You can find the MAC address for all your computers, compare them to the list, and then see if there are any devices on the list that you don’t recognize as belonging to an authorized network user.

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

If all this mucking around with MAC address and router management pages is a bit above your pay grade, not to worry. There are some third party tools that will do all the work for you. There are also third party tools that can help. One great tool is the F-Secure Router Checker.

Just navigate to the website, select the blue “Check Your Router” button and let the website do its work. It will assess any vulnerabilities in your router and alert you to them.

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

Secure your WiFi network from intruders

So what if you do identify someone using your WiFi network without your permission? It’s time to remove them and stop it happening again.

I use a Linksys Smart Router so my instructions describe that. Your router may differ slightly and use different terminology. Just adapt the following to your specific model.

  1. Log into your router and access the admin interface.
  2. Select the Wireless part of the interface or find Guest network.
  3. Turn off the Guest network unless you specifically use it.
  4. Turn off wireless. On a Linksys router, this is a toggle. This will kick everyone off your WiFi.
  5. Select WPA2 as the wireless security mode if it isn’t already selected.
  6. Change the wireless access password and save changes.
  7. Enable wireless once more.
  8. Change the password on any devices that connect to WiFi.

Turning off wireless will kick off all users at that time so you may want to alert your authorized users to avoid disruption. Once off, make sure to use WPA2, as it is currently the most secure encryption around. If your router doesn’t support WPA2, you should upgrade – it’s been around for a while and it’s the de facto standard for wireless security. (See this TechJunkie article on how to buy the right router for your needs.) Change the password to something as difficult as is practical while still being able to remember it. Mix upper and lower case, letters and numbers. If your router allows, throw in a special character or two for good measure.

Extra 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. Turn it off to stop people being able to authenticate on your network if they have physical access to the router hardware.

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

Those are the basics of how to check if someone is using your WiFi and how to stop them. Got any other ways to achieve that goal? Share them with us in the comments if so!

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