HOWTO: Detect and Defeat Wifi Intruders

Category: Wireless

Is your wireless Internet connection sometimes mysteriously slow? It's possible that you're unwittingly sharing it with a stranger. But how can you know for sure if a neighbor or a malicious hacker has tapped into your wifi? Read on to learn how you can detect bandwidth bandits, and give them the boot...

Is Someone "Borrowing" Your WiFi?

There are many possible reasons why your wireless Internet connection suddenly slows to a crawl. An unauthorized user stealing your bandwidth is one of them. It is unlikely that such a bandwidth thief will access your WiFi network if you have implemented the basic WiFi security described in my article, Wireless Network Security Checklist.

But it’s certainly a possibility that should be checked. Anyone with the skills and determination to hack your secured network is probably up to some sort of criminal activity.

There are many casual, even “innocent” bandwidth thieves who see an available network and just assume it’s OK to “borrow” it. If they are challenged for a password when they attempt to log on, they'll probably just give up and move on to another target. If you haven't bothered to assign a wifi access password, the front door to your network is wide open. If you're not sure why that's a bad idea, see The WiFi Security Mistake You Must Avoid.

Wifi Hacking

A real cybercriminal is another matter. He is out to steal something of value from you or others. He may peruse computers on your network for identity and financial information he can use or sell. He may use your Internet connection to download files illegally or hack other networks, setting you up as the fall guy when the crime is traced back to your router. This sort of crook has the tools and skills needed to defeat most WiFi security measures, especially if you have a weak password.

Windows and Apple computers have built-in utilities that show what devices are connected to your network. You can use these tools to look for unknown computers that should not be connecting to your network. Obviously, the first step is to know what devices are authorized. Each authorized computer should be assigned a computer name that you can recognize easily, i.e., "Jane PC" or "Billy Laptop". Other devices, such as printers, will have built-in names such as “HP Model 8610.” You should be familiar with what you own.

Detecting Unwanted Wifi Connections

In Windows 7 and higher, click the Start button and type “network” in the search box. Click on the word “Network” which should be the first item in the search results. A multi-part display of connected devices will appear, listing computers, media devices, network infrastructure, and other items connected to your local network. “Computers” will include PCs and Macs. “Media devices” include printers, gaming consoles, smart TVs, and the like. “Network infrastructure” includes your Internet router and/or modem. "Other Devices" will include streaming video players, such as a Chromecast or Roku.

For some reason, connected iPods, tablets and smartphones do not show up here. An unauthorized device will probably be among the “computers” listed, but if (for example) you see an Xbox that doesn’t belong to you, you obviously have an interloper. Apple OS X computers have a similar utility. You can access it via Finder > Go > Network.

Your router’s configuration program provides a better view of ALL devices connected to your network. By logging into your router, you can see a list of devices that currently have IP addresses assigned to them. Consult your router’s documentation (or Google it) to learn how to access this list. Devices that may appear in this list include desktop and laptop computers, tablets and ebook readers, iPods, smartphones, wireless printers, streaming devices such as Roku or AppleTV, gaming consoles, and television set-top boxes.

Many routers also store logs of past connections, which you can peruse to see what devices connected when you weren’t looking. If you don't know how to login to your router, or you don't know the password, ask your Internet Service Provider for help.

If you discover an unauthorized user on a secured WiFi network, my advice would be to immediately change BOTH your router login password and your wifi access password (see my Wireless Network Security Checklist link above) and then restart your router. If the intruder re-appears, it’s time to contact your Internet Service Provider, or maybe even call the cops.

Real-Time Wifi Monitoring

None of the utilities described so far alerts you when an unauthorized device connects to your network. A free third-party utility called Who's On My Wifi for Windows or Mac does, though. Running in the background, it checks your router’s network connections list at intervals that you can set, typically every two minutes. Audible and popup alerts tell you when an “unknown computer (is) found.” You can mark a device “known” and it won’t trigger an alert again. Some advanced features (including blocking unwanted devices) and technical support are available with the paid "Who’s On My Wifi Online" service, but this is not required to use the free versions.

Another option is WiFi Guard. This is a network scanning tool that checks your network connections at a user-specified interval (1-60 minutes) and alerts you if it finds any new connected devices that could possibly belong to an intruder. I found it much easier to use than Who's On My Wifi. Optionally, it can play a sound, execute a command, or send an email when an event occurs. WiFi Guard is free for Windows, and $10 for Mac.

Your thoughts on this topic are welcome! Post your comment or question below...

Ask Your Computer or Internet Question

  (Enter your question in the box above.)

It's Guaranteed to Make You Smarter...

AskBob Updates: Boost your Internet IQ & solve computer problems.
Get your FREE Subscription!


Check out other articles in this category:

Link to this article from your site or blog. Just copy and paste from this box:

This article was posted by on 22 Dec 2015

For Fun: Buy Bob a Snickers.

Prev Article:
Biggest Tech Flops of 2015

The Top Twenty
Next Article:
Geekly Update - 23 December 2015

Most recent comments on "HOWTO: Detect and Defeat Wifi Intruders"

Posted by:

David Kiwerski
22 Dec 2015

Too bad you don't mention Linux. The 'nmap' command easily shows me what/who is connected to my network. I run Linux Mint 17.3.

Posted by:

22 Dec 2015

I agree with David K., Bob. Especially since Microsoft wants everyone to employ Windows 10. Failure of it to install on one unimportant laptop convinced me to try Linux Mint and set aside the Windows 7 Home. Embracing Windows 7 early left me with useless hardware, no DVR and other problems which were tough or impossible to resolve. And when using Mint there are some Linux tutorials and forums to help smooth the rough spots. Like your Linux tutorials. In the meantime my other laptops will remain with Windows 7 until MS drops its support. Thanks.

Posted by:

Craig T
22 Dec 2015

How do I find list of connected devices in Windows 10(article only mentions Windows 7)

EDITOR'S NOTE: I said "Windows 7 and higher" which means Windows 7, 8, or 10.

Posted by:

22 Dec 2015

I tried the WIFI Guard. it has so manny add on's I will not be useing it,don't need all the garbage, thank you.

EDITOR'S NOTE: I think you may have downloaded the wrong thing. I don't see any addons in WiFi Guard.

Posted by:

23 Dec 2015

nmap exists for windows also, with the GUI it's called zenmap. It's a bit complicated to use for the common home user, but it can tell you quite a bit about every node on your network, wireless or not.

As far as the article, I don't get the reason for the applications listed at the end. If you consider using something like that I would assume you care, and if you care, why not do something like setup static leases and disable all other access to your wifi/network? That would effectively create a situation that no one else could connect to your wifi without both cracking the password AND spoofing a MAC of an existing machine. If someone goes that far to connect to your network, something like the utilities described in this article won't catch it anyway, and if the machine who's address is being spoofed is still on the network you'll have connectivity problems anyway.

Posted by:

23 Dec 2015

Bob, thank you, for this article. When I upgraded to Win 10, a couple of months back - I lost WiFi Guard. I couldn't even remember the name. I now, have it back on and I am doing my happy dance. :)

I was hacked, when I lived up in Northwest GA, about 5 years ago. I called AT&T's tech support and asked what I could do, to protect myself. I got a great tech, who worked out a solid password. At that time, your WiFi Router only gave a series of 10 or 12 numbers. He used small & capital letters, numbers, symbols and spaces.

I moved 2 1/2 years ago, to the Metro Atlanta area and about 2 weeks ago, I got a brand new router from AT&T. Boy, this is a good one, too. The password uses small & capital letters, numbers and symbols. When I saw that, I about passed out from the shock.

Finally, a manufacturer listening to customers, tech support and security guidelines! Originally, I had a 2Wire router, I now have a Pace router, which bought out 2Wire. This puppy is big and knows what it is doing. I am very pleased. :)

Posted by:

Ray Bobo
24 Dec 2015

Now I'm really confused, and concerned. I followed your instructions, but what popped up didn't look like what you described. Followed the instructions several times. First items is "View Network Computers and Devices". First time I clicked on that I saw my PC and something else I didn't recognize, but I don't recognize a LOT of thins, that's why I subscribe here. Under the word Computers, it also says: RalinKLinuxClient Properties with a PC icon beside it. Does this mean someone is connected? I clicked on that and it went away, and when I followed the instructions after that, that item was no longer there. Am I hacked? My WiFi is password protected as you instruct.

Posted by:

27 Dec 2015

I think smokey may have clicked on one of the many ads that pop-up on your site. I almost did the same thing a few times. Whoever puts those ads together has figured out how to place them and use the right colors to make one think they are downloading the app they were just reading about, when in fact they are downloading who knows what.

Posted by:

Alton James
07 Jan 2016

What does it mean if your neighbor sends something to your printer from his home. Without your Wi-Fi information?

EDITOR'S NOTE: I'd say that means your neighbor DOES have your WiFi information. How is your router protected? At a minimum, I'd recommend changing your WiFi password. Next step would be to change the router's login password.

Posted by:

16 Feb 2016

Bob & commenters share maximum security, but working with an experienced Comcast cable tech at our home for a service call upgrading our modem/router, he helped me implement some but explained why some not necessary for our home:

1) We changed our broadcast SSID internet service name not obvious to house or guessable by hacker.
2) We strengthened our wifi password per Bob's links' instructions, noting to change occasionally.
3) We changed our Comcast modem/router password to a strong unique one for our home, written on a Post-It note under modem so techs can service!
4) Verified Comcast encryption best WPA2+AES.
5) Reduced number of local IP addresses down to 8 tech advised, "leaving a few extra for in case old addresses still in use here."
6) We didn't limit our wifi to only our home devices' "SSN" 'Mac' addresses preventing tech service here with their devices!
7) We haven't yet downloaded/installed WiFi Guard to alert of intruders.
8) If intruder breaks through this we'll immediately change both passwords & call Comcast as Bob instructed; & maybe implement these ultra tips more. Thank you! We feel better educated & safer now :)

Post your Comments, Questions or Suggestions

*     *     (* = Required field)

    (Your email address will not be published)
(you may use HTML tags for style)

YES... spelling, punctuation, grammar and proper use of UPPER/lower case are important! And please limit your remarks to 3-4 paragraphs. If you want to see your comment posted, pay attention to these items.

All comments are previewed, and may be edited before posting.

NOTE: Please, post comments on this article ONLY.
If you want to ask a question click here.

Free Tech Support -- Ask Bob Rankin
RSS   Add to My Yahoo!   Feedburner Feed
Subscribe to AskBobRankin Updates: Free Newsletter
Copyright © 2005 - Bob Rankin - All Rights Reserved
Privacy Policy -- See my profile on Google.
[an error occurred while processing this directive]

Article information: AskBobRankin -- HOWTO: Detect and Defeat Wifi Intruders (Posted: 22 Dec 2015)
Copyright © 2005 - Bob Rankin - All Rights Reserved