Preventing automatic restart

I'm intensely angry right now, I'm having a great deal of difficulty
maintaining my composure, so this might be a bit unfocused.

I just came back to my PC, having been away for less than 20 minutes, to
find that it had restarted itself after downloading an update. I had at least
a dozen documents open on the machine and a VMWare virtual session running
that I was using to work with an IDE.
None of it was saved to disk. My machine is attached to a UPS, and I
routinely use the Sleep function to carry on where I left off the previous
night. I've lost - God knows - days and days of work because Windows decided
it would close everything down without my consent.

I wouldn't be surprised if the update was just another revision of the vile
Genuine Advantage application. I don't want to check because if I discovered
that to be the case I wouldn't be held responsible for my actions. What an
unbelievably awful, stupid, irresponsible 'feature'. I don't even want to
contemplate how much work I'm going to have to redo, the last few days have
been a nightmarish grind.

Thanks Microsoft, you've left me feeling shellshocked and dispairing.

How can I stop this from ever happening again?