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So far, Stuxnet has infected at least 45,000 industrial control systems around the world, without blowing them up – although some victims in North America have experienced some serious computer problems, Eric Byres, a Canadian expert, told the Monitor. Most of the victim computers, however, are in Iran, Pakistan, India, and Indonesia. Some systems have been hit in Germany, Canada, and the US, too. Once a system is infected, Stuxnet simply sits and waits – checking every five seconds to see if its exact parameters are met on the system. When they are, Stuxnet is programmed to activate a sequence that will cause the industrial process to self-destruct, Langner says.

Langner's analysis also shows, step by step, what happens after Stuxnet finds its target. Once Stuxnet identifies the critical function running on a programmable logic controller, or PLC, made by Siemens, the giant industrial controls company, the malware takes control. One of the last codes Stuxnet sends is an enigmatic “DEADF007.” Then the fireworks begin, although the precise function being overridden is not known, Langner says. It may be that the maximum safety setting for RPMs on a turbine is overridden, or that lubrication is shut off, or some other vital function shut down. Whatever it is, Stuxnet overrides it, Langner’s analysis shows.

"After the original code [on the PLC] is no longer executed, we can expect that something will blow up soon," Langner writes in his analysis. "Something big."

For those worried about a future cyber attack that takes control of critical computerized infrastructure – in a nuclear power plant, for instance – Stuxnet is a big, loud warning shot across the bow, especially for the utility industry and government overseers of the US power grid.

"The implications of Stuxnet are very large, a lot larger than some thought at first," says Mr. Assante, who until recently was security chief for the North American Electric Reliability Corp. "Stuxnet is a directed attack. It's the type of threat we've been worried about for a long time. It means we have to move more quickly with our defenses – much more quickly."

Has Stuxnet already hit its target?It might be too late for Stuxnet's target, Langner says. He suggests it has already been hit – and destroyed or heavily damaged. But Stuxnet reveals no overt clues within its code to what it is after.

A geographical distribution of computers hit by Stuxnet, which Microsoft produced in July, found Iran to be the apparent epicenter of the Stuxnet infections. That suggests that any enemy of Iran with advanced cyber war capability might be involved, Langner says. The US is acknowledged to have that ability, and Israel is also reported to have a formidable offensive cyber-war-fighting capability.

Could Stuxnet's target be Iran's Bushehr nuclear power plant, a facility much of the world condemns as a nuclear weapons threat?

Langner is quick to note that his views on Stuxnet's target is speculation based on suggestive threads he has seen in the media. Still, he suspects that the Bushehr plant may already have been wrecked by Stuxnet. Bushehr's expected startup in late August has been delayed, he notes, for unknown reasons. (One Iranian official blamed the delay on hot weather.)

But if Stuxnet is so targeted, why did it spread to all those countries? Stuxnet might have been spread by the USB memory sticks used by a Russian contractor while building the Bushehr nuclear plant, Langner offers. The same contractor has jobs in several countries where the attackware has been uncovered.

"This will all eventually come out and Stuxnet's target will be known," Langner says. "If Bushehr wasn't the target and it starts up in a few months, well, I was wrong. But somewhere out there, Stuxnet has found its target. We can be fairly certain of that."

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