Countdown to Zero Day: Stuxnet and the Launch of the World's First Digital Weapon

by Kim Zetter

Now that the Symantec team—minus Falliere, who had left Symantec for a job at Google—had their hands on this early variant, they were finally able to determine what the 417 PLCs were controlling and what Stuxnet was doing to them. It turned out this version was targeting the valves that managed the flow of uranium hexafluoride gas into and out of the centrifuges and cascades at Natanz.29 Stuxnet was opening and closing the valves to increase the pressure inside the centrifuges to five times its normal level. At that pressure, the gas would likely begin to solidify, ruining the enrichment process, and causing the centrifuges, spinning at high speed, to careen dangerously off balance and crash into other centrifuges around them. Or at least this was likely the plan. It may not have worked as well or as quickly as the attackers had hoped, so in 2009 they changed tactics and focused on attacking the frequency converters instead—a more direct method of damaging the centrifuges.