The Iranian Nuke plant control computers are most likely running Linux (there is a US trade embargo on Iran, so probably wouldn't be able to get a Windows License ). A most sensible precaution when running a high risk project such as a civilian nuclear plant which foreign powers have been threatening to destroy for some time now.

What is potentially worrying though is the fact that many of the computer system for the US and UK nuclear deterrent (sorry its a word that has gone out of fashion lately since the end of the cold war) such as the Trident Nuclear submarines use Windows 2000.

I think I've got a terminal services window running right now. (only kidding NSA...)

As for the Grid going down in the USA due to a hacking and malicious typing of del *.* in a DOS window using Remote desktop help (the Mongolian sitting in his yurt), its these guys you have to worry about.

http://www.youtube.com/watch?v=q1fFivb5qFs