When the worm found converter drives operating between 807 Hz and 1210 Hz, Stuxnet reset the frequency to 1410 Hz, then after 27 days, dropped the frequency to just 2 Hz and later bumped it up to 1064 Hz. It then repeated the process.
After Symantec released its latest findings, experts noted that the 807-1210 Hz range was consistent with drive converters used to power gas centrifuges, and that the changes Stuxnet ordered could hamper enrichment efforts or cause the high-speed rotors inside the centrifuges to fly apart.
Symantec's analysis gained credence last week when the International Atomic Energy Agency (IAEA), the United Nations' nuclear watchdog, reported that earlier this month Iran had stopped feeding uranium hexafluoride gas to its centrifuges for about a week. Speculation quickly focused on problems created by Stuxnet as the reason for the shutdown.
But the same day that the IAEA report made news, Ali Akbar Salehi, the head of Iran's nuclear agency, denied Stuxnet had affected the country's atomic program . According to the Associated Press, which quoted the official IRNA news agency, Salehi said Iran's "enemies failed to achieve their goals" with the worm.
"We discovered the virus exactly at the same spot it wanted to penetrate because of our vigilance and prevented the virus from harming [equipment]," Salehi told the IRNA.
Since September, Iranian officials have acknowledged that Stuxnet had spread through Iran and infected tens of thousands of PCs, including several personal computers owned by employees at the Bushehr nuclear power plant.
But until Monday, Iran had repeatedly denied that malware had managed to infiltrate its nuclear program and caused any damage or disruption. Two months ago, for instance, the deputy head of Salehi's agency claimed Stuxnet had not penetrated Iran's nuclear facilities.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is firstname.lastname@example.org .
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