Langner thinks that it's possible that Bushehr may have been infected through the Russian contractor that is now building the facility, JSC AtomStroyExport. Recently AtomStroyExport had its Web site hacked, and some of its Web pages are still blocked by security vendors because they are known to host malware. This is not an auspicious sign for a company contracted with handling nuclear secrets.

One of the things that Langner discovered is that when Stuxnet finally identifies its target, it makes changes to a piece of Siemens code called Organizational Block 35. This Siemens component monitors critical factory operations -- things that need a response within 100 milliseconds. By messing with Operational Block 35, Stuxnet could easily cause a refinery's centrifuge to malfunction, but it could be used to hit other targets too, Byres said. "The only thing I can say is that it is something designed to go bang," he said.