William J. Broad, John Markoff and David E. Sanger
NY Times 
Jan 16, 2011
The Dimona complex in the Negev desert is famous as the heavily guarded heart of Israel’s never-acknowledged nuclear arms program, where neat rows of factories make atomic fuel for the arsenal.
Over the past two years, according to intelligence and military experts familiar with its operations, Dimona has taken on a new, equally secret role — as a critical testing ground in a joint American and Israeli effort to undermine Iran’s efforts to make a bomb of its own.
Behind Dimona’s barbed wire, the experts say, Israel has spun nuclear centrifuges virtually identical to Iran’s at Natanz, where Iranian scientists are struggling to enrich uranium. They say Dimona tested the effectiveness of the Stuxnet computer worm, a destructive program that appears to have wiped out roughly a fifth of Iran’s nuclear centrifuges and helped delay, though not destroy, Tehran’s ability to make its first nuclear arms.
“To check out the worm, you have to know the machines,” said an American expert on nuclear intelligence. “The reason the worm has been effective is that the Israelis tried it out.”