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It's been a while since, every now and then, I see a pop-up window appearing for a few milliseconds, that then disappears. I don't even have the time of reading what it says.

Any idea on what could that be?

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This happens frequently on file sharing services, for example. Download buttons trigger some JS code which open one or more "pop-under" windows (they show up for a few miliseconds and hide behind the main window). If you use the default shortcut to switch between app windows, Cmd + `, you'll probably find some hidden ad windows. Most of the time, built-in browser pop-up blockers and third party extensions will fail to block these windows, since web developers continue to find new and exciting ways to annoy users. – user36018 Jul 31 '14 at 14:59
up vote 1 down vote accepted

Is it when you launch an application?

I have a similar behavior with jDownloader, and it seems to be the Firewall (Allowing the app to make a connection) popup.

I don't have a solution, it's still happening, but since I don't have any trouble using the app, I haven't looked further.

Since the app is based on Java, maybe OS X Lion notice (after showing the popup) that Java is allowed to connect and cancel the prompt. It's purely based on assumption and I wouldn't be surprise to be proven wrong but I can't find any other reason (since it's only with this, Java-based, app that it's happening)

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that happens with Chrome, but I must say that I use my mackbook almost exclusively for internet browsing – Bob Apr 10 '12 at 18:23

Go to System Preferences>Security & Privacy>Firewall>Firewall Options and add an incoming service: Library/Java/Home/bin/java

Save settings/close the are done.

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Hmm, hard to tell without more detail.

The first thing to try and track down is which application is causing the windows to open. If you quit Safari (or whatever your browser is) and leave it closed for a while do the windows stop appearing?

If it's not your browser, you could try launching 'Activity Monitor' (found in the /Applications/Utilities folder) and try spotting processes that you don't recognise. it could be one of those.

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As said in the comment above, it happens with Chrome, but I use my mac for internet only (almost). I will try to monitor and see what happens. I just hope it's not a virus. – Bob Apr 10 '12 at 18:24

My Windows 7 Home Premium had popups appearing and disappearing in a flash after reinstallation. The mysterious popups went away after I turned Windows Firewall on.

It did not fix it - just slows down the frequency. I just discovered that running the process monitor stops the pop ups. Each time it happens, I start the process monitor and it will leave me alone until the next time I turn the computer on.

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Where is Apple product in all this? – Buscar웃 Oct 18 '14 at 23:01

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