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Why does the mouse on one computer move the pointer on another?


When my son uses his mouse on his laptop upstairs it moves the mouse on the computer downstairs? Can you help?

I’m not certain that I can, but I can certainly give you a few things to look into.

The real reason I’m addressing this question is that it raises a very interesting privacy issue that most people aren’t aware of.

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You would probably realize if this were the case – since you’ll have had to install the software – but remote-control software like VNC or similar tools can cause exactly this behaviour, because … well, because that’s exactly what they’re designed for. As I type right now, I have on my desktop computer a window that is the desktop of my Mac laptop being controlled remotely:

VNC Window in Windows XP connected to my Mac

“Wireless mice use short distance radio signals to send the mouse’s instructions to the computer.”

If I move the mouse within that window on the desktop the pointer on the laptop itself moves as well, since I’m controlling it remotely. Similarly, if I type into that window it goes to the remote computer. (Remote Desktop connection wouldn’t apply here since the actual laptop screen would show the login screen rather than the actual desktop while it’s in use. With VNC and other remote control solutions you’ll simply see your computer as if it’s acting on its own while being remotely controlled.)

But like I said, since that typically requires some setup, you’d probably know if it were the case.

The scenario that’s a little less obvious are wireless mice.

Wireless mice use short-distance radio signals to send the mouse’s instructions to the computer. Similarly, wireless keyboards do the same.

The problem is that it’s transmitting, so anyone in range in theory could “listen in” to signals being sent. To overcome that, various keyboard and mouse manufacturers have established a kind of handshake that is supposed to allow the mouse or keyboard to actually connect to only one computer. And finally, the data being transmitted may, or may not, be encrypted.

So, for the practical problem you’re experiencing, use a different mouse on that laptop and see if that doesn’t resolve the issue. Disconnecting any external mouse and using the internal mouse, or using a wired one would be best, at least for that initial test.

But let’s address the security issue we just raised.

  • your wireless keyboard or mouse is transmitting, and anyone “in range” could listen in
  • your wireless keyboard or mouse may not be encrypting its data (or may be doing so poorly), so anyone “in range” can see what you’re typing if they listen in
  • “in range” varies on many things but could be as little as 30 feet, or as much as 300.

I’ve actually heard of this type of wireless eavesdropping being used in corporate environments.

So, what to do?

Well, I don’t want to foster undue paranoia – more often than not this is not happening.

My advice is simply to be aware. If you’re in a sensitive environment, consider a wired mouse and/or keyboard, or use your laptop’s internal mouse and keyboard which are, by definition, wired. If you need a wireless device, look for strong encryption to be called out – but do some research since certain forms of wireless keyboard encryption have in fact also been hacked and could still be sniffed.

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5 comments on “Why does the mouse on one computer move the pointer on another?”

  1. I had never considered this but I am also not paranoid nor have a need to be.

    I have been glancing at wireless keyboards and mice for a girlfriend’s laptop and have not noticed encryption being specified. I will look at that more closely in the future.

  2. I had this in a hotel reception where I look after the computers and it simply turned out to be that one PC was using the same frequency as the wireless mouse receiver on the other PC. Both were the same brand and model. The receptionist was going crazy when I was using the mouse on one machine nearby and it was moving the mouse on both! I simply reset the mouse receiver and mouse using the reset buttons which created a new frequency. The problem didn’t return.

  3. Great topic, I will make sure I stay away from wireless peripherals.

    That’s an extreme reaction. I love wireless peripherals. Just make sure to understand the risks depending on the environment you happen to be in. In most cases there’s no issue.


  4. I have a similar problem. I have 2 Imacs (M3) in the same office. Randomly while using the mouse the cursor will stop moving on Imac A and the cursor on the imac B will be moving from the mouse. Sometimes it is Imac B that has the mouse and suddenly it will be moving the cursor on Imac A. We have 2 sets of mice. One set is bluetooth & one is a generic mouse connects with a USB wart. These USB wart mice never stepped on each other with the older Imacs they were on, but now they do. I surmise that this is a network problem and not a bluetooth problem because it happens without respect to which mouse is plugged in at the time. Both computers are logged into the same username. It is not consistent. One only notes a problem when the cursor stops moving when one is moving the mouse and then the person across the room mentions that their cursor if moving and they are not moving it. I don’t know what to do.

  5. This article is 15 years old. I wonder if this is still a problem. Because of wireless sniffing, keyboard manufacturers have switched to encrypted connections. I’m not sure if that also applies to wireless mice.

    Now that computer mice no longer have tails, why do we still call them mice? We should call them turtles.


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