malware - How can I indentify this invisible window on my desktop?

There's an invisible window of some application on my desktop and the only thing detectable about it is its borders as seen in the image below. The window or its edges are not clickable.

I'm guessing this could be some malware so I need to identify which application is drawing that window. So far, I've gone through the list of running processes in Task Manager to see if something looks suspicious and have scanned the PC with Malwarebytes Anti-Malware to no avail. I also tried using Process Explorer's drag over window tool and it just detects explorer.exe. Could this be a bug in explorer? I'm running Windows 10.