[link to www.nytimes.com]

Worm Was Perfect for Sabotaging Centrifuges
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The new forensic work narrows the range of targets and deciphers the worm’s plan of attack. Computer analysts say Stuxnet does its damage by making quick changes in the rotational speed of motors, shifting them rapidly up and down.

Changing the speed “sabotages the normal operation of the industrial control process,” Eric Chien, a researcher at the computer security company Symantec, wrote in a blog post...

a study released Friday by Mr. Chien, Nicolas Falliere and Liam O. Murchu at Symantec, concluded that the program’s real target was to take over frequency converters, a type of power supply that changes its output frequency to control the speed of a motor.

The worm’s code was found to attack converters made by two companies, Fararo Paya in Iran and Vacon in Finland. A separate study conducted by the Department of Homeland Security confirmed that finding, a senior government official said in an interview on Thursday.

Then, on Wednesday, Mr. Albright and a colleague, Andrea Stricker, released a report saying that when the worm ramped up the frequency of the electrical current supplying the centrifuges, they would spin faster and faster. The worm eventually makes the current hit 1,410 Hertz, or cycles per second — just enough, they reported, to send the centrifuges flying apart.

In a spooky flourish, Mr. Albright said in the interview, the worm ends the attack with a command to restore the current to the perfect operating frequency for the centrifuges — which, by that time, would presumably be destroyed.

“It’s striking how close it is to the standard value,” he said.

The computer analysis, his Wednesday report concluded, “makes a legitimate case that Stuxnet could indeed disrupt or destroy” Iranian centrifuge plants.