Spyware / Backdoor ?

Hi all,

this morning I booted the PC and went away. When I came back I saw a black box in the left upper corner like a cmd window, but empty. Then this black window vanished and I didn't think about that.

Now I started the PC again and I saw, that the program symbols on the desktop are reorganized - according to the size of the black window I saw in the morning.

 

For me it looks, that there was an external access like Windows remote desktop connection with a smaller screen resolution - that would be the answer to the reorganized desktop.

 

I already did a Norton Quick Scan - without success, the complete system scan is still running, but up to now without access, too.

 

Anybody an idea, what this could have been?

 

thanks a lot!