"The NSA and Israel cowrote it," he told Der Spiegel in an email interview conducted before he publicly outed himself as the NSA mole. Snowden is currently in Russia and a "free man" according to Vladimir Putin – as long as there are no further NSA leaks.
The Stuxnet code, which has been deployed since 2005, is thought to be the first malware aimed specifically at damaging specific physical infrastructure*, and was inserted into the computer networks of the Iranian nuclear fuel factory in Natanz shortly after it opened.
Early variants attempted to contaminate uranium supplies by interfering with the flow of gas to the fuel being processed, potentially causing explosive results in the processing factory. Later a more advanced variant attacked the centrifuges themselves, burning out motors by rapidly starting and stopping the units and contaminating fuel production, although it may actually have encouraged the Iranians.
Last year an unnamed US official said that Stuxnet was part of a program called Operation Olympic Games, started under President Bush and continued under the current administration, aimed at slowing down the Iranian nuclear effort without having to resort to risky airstrikes. General James Cartwright, a former vice-chairman of the Joint Chiefs of Staff, is currently under investigation by the US government for allegedly leaking details of Operation Olympic Games.