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I get this popup:

Stop running this script?

It looks rather suspicious since it refers to "web browser" rather than a specific product, and doesn't offer any other details or identifying information.

I've tried to figure out what dastardly deed it could be doing and all I can think of is that it could be somehow superimposed over a Windows security authorization request (though I have no idea how one would do that).

Added: I got this in the late phases of a reboot after a crash (some Microsoft mystery). To my recollection, no browser was active when the system crashed, and I don't have anything set to autostart on boot.

I'll also add that I checked Process Explorer while the message was up and saw no sign of Mozilla (my usual browser). I forget what (if any) task bar name may have been displayed, but it was not useful.

I tried X-ing the box, but that was ignored, so I clicked "No" once. The window went away and then popped up about an inch to the left and higher up. Clicked "No" again and it went away.

I have seen a similar screen when using a browser on a bad web page, but to my recollection it always identified the browser, and the web page/script was obvious from the context.

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Though when I bring up a Windows authorization request the two windows don't line up. – Daniel R Hicks Apr 5 '12 at 13:15
UAC is designed so it will always be on top and other applications won't be active during an elevation request (secure desktop), so that's probably not related. – Bob Apr 5 '12 at 13:20
Do you get that while browsing, or doing other things? If its while browsing, what browser are you using? Can you provide the page you are on? I can tell you Firefox will not show that, and Microsoft says Internet Explorer's message contains the browser name. Oddly enough, a Google search for that exact error comes up with legitimate sounding results (web designers wondering why their JavaScript is running too slowly). – Bob Apr 5 '12 at 13:27
When a UAC prompt is displayed, a screenshot is taken of your current desktop, then everything is basically sent to the background until the user interacts with the prompt or enough time has passed and windows automatically closes it. – Ramhound Apr 5 '12 at 13:41
As long as you had Process Explorer open, you could have used its Find Window Owning Process feature (a bullseye-looking icon up on the taskbar). – kreemoweet Aug 7 '12 at 5:03
up vote 2 down vote accepted

It's just a popup.

<script language="VBScript">
    Sub myAlert(title, content)
        MsgBox content, 0, title
    End Sub

<script type="text/javascript">
    myAlert("Web Browser", "Stop running this script?\n\nA script on this page is causing your web browser to run slowly. If it continues to run, your computer might become unresponsive.");

Either by the code above, which works in Internet Explorer, or an actual slow running script can produce that alert. It is pretty much legit and I believe it rather to be an actual slow running script, because who in his right mind would reproduce that box using VBScript?

It's not scam or malware.

They don't ask such stupid questions, clicking on Yes or No won't suddenly install something on your PC.

At best, it is just a joke that you can safely ignore...

What does the Internet Explorer warning look like?

Execute the following in your address bar and wait for a minute or so: javascript:while(true);

share|improve this answer
Except it does not match up with the error message in Microsoft's KB article for IE8 and previous, and IE9 doesn't even use popups. It has a bar down the bottom saying the page has stopped responding and a button to recover the page. It is most likely not dangerous, but it is also a little odd. – Bob Apr 5 '12 at 13:42
@Bob: Perhaps another application uses Javascript? Because it looks the same part from the title. – Tom Wijsman Apr 5 '12 at 13:46
Then I guess the goal is to find this other application, unless an alternative "web browser" is being used. DanH: does something you do trigger the popup, or does it just appear 'randomly'? – Bob Apr 5 '12 at 13:50

Somebody wrote a bad javascript, with an infinite loop or other CPU-intensive process. Those are usually easy to detect during development, but in a more complex scripts oopsies like this happen sometimes. I've done my share of those... annoying, but harmless.

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This looks to me like a scam or malware. No matter how badly things go in a browser script, browsers today are designed as sandboxes, segregating their code completely from the rest of the OS operation.

Another clue is the window title "web browser". Windows applications identify themselves by name ("Firefox", "Chrome" etc.) not by a generic family type. This was clearly written by someone who doesn't even know (nor care) which browser you're running.

Here's what I'd do if I see that message again: run Process Explorer, and find out which process owns this window. I bet it's a malware/virus/spam app. Use a good antivirus to kill it.

Update: Several people commented below that this is a normal browser message. I haven't seen this kind of text, or threat to the general OS behavior coming out from a browser ever - but, generally speaking, I haven't seen everything yet, and it might be a legit script result. If that were the case, than looking at the Window's source app (as I mentioned above) would just show you your browser's process name. At which point, you can safely close the browser window showing the message, as it is indeed a Javascript message.

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How is this scam or malware? Please note that the title is not necessarily set by the application and that the application might choose another title for message boxes if it wants to. It is pretty much possible that this is a legit message box, because a script ran slow. You won't find any process... – Tom Wijsman Apr 5 '12 at 13:31
This is some of the worst advice I have seen in over 15 years dealing with computers. This prompt certainly is NOT malware, there is no evidence to support that claim, this prompt happens when some script runs poorly. – Ramhound Apr 5 '12 at 13:43

I would like to chime in at the fact this could potentially be caused due to a malicious script, or the remenants of one. I was browsing the net, a pop-up window came and instant notification of java update popped up (looked phoney), clicked no to allow script/update/whatever, continued browsing and then got the Interpol Virus. Trojan.Siredef.c and Trojan.Reveton had infected my system.

After several scans and such I have removed the infection from my system (not entirely yet), although now I am stuck with these "stop running script" messages popping up seemingly at random, and an error message stating the file name of the Trojan could not start (quarantined). It is possible due to the missing files associated with the script of the removed/quarantined malware could be causing the error message.

Maybe someone can suggest a great tool to scan for the ghost remenants of viruses on one's system that could cause this message to pop up?

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