Confirmed: Stuxnet worm perfectly designed to disable nuclear centrifuges

The paternity of the worm is still in dispute, but in recent weeks officials from Israel have broken into wide smiles when asked whether Israel was behind the attack, or knew who was. American officials have suggested it originated abroad.

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…

Until last week, analysts had said only that Stuxnet was designed to infect certain kinds of Siemens equipment used in a wide variety of industrial sites around the world. But 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.