Can't click the non-existent "Cancel" button. Pressing Escape is the same as pressing Enter. This is a Modal window, which means I can see the Netflix movie still playing in the gray transparent background.
Oh, and if you interact in any way with this "Dialog" box, it automatically starts downloading and installing whatever updates it talks about, without confirmation that you want to do it or not. Oh, and rebooting (either via CAD or unplugging) doesn't get rid of it either, pops right back up as soon as you log on.
My only saving grace is that I force updates to never install automatically via Group Policy, but apparently that doesn't preclude this message from showing up. So, I just have to hit the button, ignore the "You can't install updates at this time" error, and go back to what I was doing.
Every hour.