I have an app that, in some cases, when an action is performed, a white-box appears in the upper-left corner. You can't move it, but it allows for resizing and only disappears if you close the browser and open it again.
Sounds like you may need a virus and spyware scan.
The browser is IE and the app is an internal-app that talks with a Mainframe app. The white-box only appears when we interact with the Mainframe.