Researchers have found that the Stuxnet worm that struck computer systems around the world, and Iranian systems in particular was a pretty ingenious design that would wreck the enrichment centrifuges by changing the speeds at which they operate to throw them out of calibration:

Experts dissecting the computer worm suspected of being aimed at Iran’s nuclear program have determined that it was precisely calibrated in a way that could send nuclear centrifuges wildly out of control.

Their conclusion, while not definitive, begins to clear some of the fog around the Stuxnet worm, a malicious program detected earlier this year on computers, primarily in Iran but also India, Indonesia and other countries.

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.

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.

Those fluctuations, nuclear analysts said in response to the report, are a recipe for disaster among the thousands of centrifuges spinning in Iran to enrich uranium, which can fuel reactors or bombs. Rapid changes can cause them to blow apart. Reports issued by international inspectors reveal that Iran has experienced many problems keeping its centrifuges running, with hundreds removed from active service since summer 2009.

“We don’t see direct confirmation” that the attack was meant to slow Iran’s nuclear work, David Albright, president of the Institute for Science and International Security, a private group in Washington that tracks nuclear proliferation, said in an interview Thursday. “But it sure is a plausible interpretation of the available facts.”