Last month there was an article about a virus that targetted Iran’s Nuclear Research. There’s a little more on Stuxnet worm in the NY Times.
From Stuxnet Worm Used Against Iran Was Tested in Israel:
The computer program also secretly recorded what normal operations at the nuclear plant looked like, then played those readings back to plant operators, like a pre-recorded security tape in a bank heist, so that it would appear that everything was operating normally while the centrifuges were actually tearing themselves apart.
Pete Ware 