Windows 10 Small static window appears

[terjemk]

All of a sudden this litte window appears on top of all other windows. See screenshot.

Does anybody know what this is and how to get rid of it?

 

[livix07]

It might be caused by an add-on or even a virus.

Does it appear even when you don't use the web browser? what web browser do you use?

 

[Neemobeer]

Download process explorer Process Explorer - Windows Sysinternals. Click the black cross-hair icon and drag the mouse over that window and release the mouse. It should identify the process of the Window as well as any parent process that spawned it.