The target was seemingly impenetrable; for security reasons, it lay several stories underground and was not connected to the World Wide Web. And that meant Stuxnet had to act as sort of a computer cruise missile: As it made its passage through a set of unconnected computers, it had to grow and adapt to security measures and other changes until it reached one that could bring it into the nuclear facility.
When it ultimately found its target, it would have to secretly manipulate it until it was so compromised it ceased normal functions.
And finally, after the job was done, the worm would have to destroy itself without leaving a trace.
That is what we are learning happened at Iran's nuclear facilities -- both at Natanz, which houses the centrifuge arrays used for processing uranium into nuclear fuel, and, to a lesser extent, at Bushehr, Iran's nuclear power plant.
At Natanz, for almost 17 months, Stuxnet quietly worked its way into the system and targeted a specific component -- the frequency converters made by the German equipment manufacturer Siemens that regulated the speed of the spinning centrifuges used to create nuclear fuel. The worm then took control of the speed at which the centrifuges spun, making them turn so fast in a quick burst that they would be damaged but not destroyed. And at the same time, the worm masked that change in speed from being discovered at the centrifuges' control panel.
At Bushehr, meanwhile, a second secret set of codes, which Langner called “digital warheads,” targeted the Russian-built power plant's massive steam turbine.
Here's how it worked, according to experts who have examined the worm:
Originally Posted by AdamG
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