I have an intrusive app popping up unbidden on my PC (Windows 11) which is an almost completely blank square in the middle of the screen. It doesn’t respond to any clicks and refuses to accept a subordinate position among tiled windows.
I’ve gone to my installed apps in my settings but I obviously can’t identify it on the list and I’m afraid of deleting something that might be critical. Any suggestions from my computer betters?
(If this is the wrong forum, noble mods, please feel free to move)
You could look into the autostart section in task manager for suspicious apps: right-click on the task bar, click on task manager, look for “autostart” in the list on the left hand side of the window and check the apps in the list: does any of them look unknown, fishy or otherwise suspicious? If you’re not sure, you could make a screenshot and post it here, but be aware that this would be a privacy issue, because we all could see the apps that autostart on your system.
ETA: I just had a crazy thought: might the “app” just be a desktop background picture you accidentally set up? Hit the Windows key+I to open the settings, go to “Personalisation”, then “Background”, and look if “Picture” is set. If yes, set it to “Full Color” and see if the “app” disappears.
This is a good suggestion, and even before looking into the Startup apps, just take a look at currently running apps. Next time you see that blank square, open task manager and look at what’s under the Apps node in the list of processes. Post the list here and we can see if anything looks weird.
I might also suggest that you take the computer to a local shop to have them do a deep scan and clean on it (or do it yourself with a malware scanner, if you’re comfortable).
If you have one bad app like that, chances are you have others too, and it’s better to remove all of them (and update & secure whatever you need to to prevent future occurrences).
Today it might just be a blank square, but the next time it might be ransomware or a login stealer 
Have you installed anything recently, and then noticed the pop up? You can uninstall that last application. Have you been to any website you don’t normally go to (no judgements)?
Thanks to you all for your responses.
The intrusive app has disappeared and the only action I’ve taken since posting was re-enabling Windows Defender. Which I can only think got disabled inadvertently during a brief complication while cancelling Microsoft Office (reference the thread a while back about the subscription price for Office doubling; I have since moved on with Libre Office).
Still, I remain a little concerned about the possibility of something sinister lurking in the background.
I would not be surprised if the blank window was a faulty Windows prompt telling you to re-enable Defender.