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Is there any way to send a popup message from a Linux system to a "random" laptop/tablet/mobile linked to my Wireless network? For example, if I let my WLAN open and I see an unrecognized computer connected to it, is there a way to send a message to that device?

On the other hand, if I am connected to someone else's open network and they may or may not be aware that their network is open, can I send them a message warning that I am accessing their network?

Probably for a completely "random" device the answer should be no. But if we restrict to laptops with Win7 or Linux SO is there any service running by default on such systems that allows one to send such popup messages?

PS: I have no practical motivation for this question. This is only a curiosity.

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If someone connects to your open WLAN, to what purpose would you like to send him a message ? –  HQarroum Mar 29 '12 at 7:08
    
You could do something like this with a proxy/gateway. Have your internet traffic all go through this server. You can shape and mold the traffic as you see fit. –  kobaltz Mar 29 '12 at 23:16
    
As far as sending someone else a message when joining their network, I'm unsure how you would go about that. Do you have administrative access to the network you would be accessing? –  kobaltz Mar 29 '12 at 23:17
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possible duplicate of Is it possible to communicate to other WiFi users in the house? –  Diogo Mar 29 '12 at 23:20
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@DiogoRocha thanks for point me out that post. It indeed answer the question. –  Leandro Mar 29 '12 at 23:37

4 Answers 4

up vote 4 down vote accepted

Short answer: No, this is not possible.

As mentioned in one of the answers in the question linked by Diogo Rocha, there was a tool called net send for windows machines, but I don't know it was installed by default.

I would be very very worried about the security of my system if it was possible to open some popup remotely on my screen. Excluding possible security leaks there is no default way to do this on either windows or linux.

One thing you could do is manipulate the other users webtraffic. like explained here

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thanks for the answer Walter and the link. I liked the link a lot, very funny :) –  Leandro Mar 29 '12 at 23:41
    
Messenger (which listens for net send) was disabled by default in Windows XP SP2. Before that, it generally worked. –  Eroen Mar 29 '12 at 23:53

i have just started studying for computer engg.. but still i want to answer this Que.. it might be helpful .. ans:- if connected user , using windows vista/7 then try this command in windows vista/7 in cmd...

 ***msg /server:( here connected user IP/PC-name ) * /time:( in seconds ) " message"***

 this will create a popup msg to connected user
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This is essentially net send and as such will not work. –  Daniel B Jul 22 at 6:32

TL;DR: No, but...

It wouldn't be easy, because different operating systems use different mechanisms for such things.

Most Linux distributions wouldn't support it anyway - even if the machine were running something you could hook into it'd require you to authenticate as a valid user, and .zo'o if you could do that automatically for arbitrary machines you'd probably already have taken over half the internet.

I couldn't tell you about an OSX-based "alien", but I suspect it'd be similar.

Windows, I believe, has a standard mechanism for sending a popup message to another machine, but IIRC it still requires authentication (although so many people leave their Administrator accounts without a password...).

What you could do is run an intercepting proxy (Squid is good for this sort of thing) that shows the desired message as the first page of any browsing session that's from an IP on a whitelist, and configure your router to give known machines consistent IPs based on their MAC addresses. Most routers have this function, but otherwise you could use static addressing for known machines and set the router's DHCP pool to something smaller than the usual 253 addresses to prevent collisions.

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I' am using currently a WRT-160 router and it seems that is possible to used your suggestion. Thanks for the information Darael. –  Leandro Apr 3 '12 at 2:12

Other device must have the messenger service as active (Windows XP, Windows Vista and earlier) or computer should have other, net send compatible messenger like Lantalk XP and others. Your wifi router should be able to pass broadcast packets.

After that you'll be able to send popup via SAMBA (smbclient -M), target name is * (for all in your subnet). However, messenger service has been disabled by default since the XP SP2. Net send compatible messengers is also out of business and unlikely will be used at home (not in the office network).

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