I have absolutely no idea what is causing this.
I have a Windows 7 Professional box, and sometimes (I don't know under which circumstances), hitting ctrl-c (for example, to copy something into the clipboard) initiates an immediate system shutdown. All running applications immediately close (even faster than if I had started a shutdown from the start menu), and the system shuts down.
I've been able to abort this with some apps like PuTTY that refuse to close unless I confirm that I do want to close them. Hitting "no" successfully aborts the system shutdown, but not before having closed a dozen or more other applications I was working on.
I suppose this is not default behavior (although I'm not sure if this happens when the desktop is the focused window). I have checked for viruses with an up-to-date antivirus, and same for spyware. I am an IT professional, so I think I know what I'm doing.
Maybe this is being caused by some software. Does anybody know of any software that does this so I can at least find the culprit?