The construction of the worm was so advanced, it was “like the arrival of an F-35 into a World War I battlefield,” says Ralph Langner, the computer expert who was the first to sound the alarm about Stuxnet. Others have called it the first “weaponized” computer virus…

–Once allowed entry, the worm contained four “Zero Day” elements in its first target, the Windows 7 operating system that controlled the overall operation of the plant. Zero Day elements are rare and extremely valuable vulnerabilities in a computer system that can be exploited only once. Two of the vulnerabilities were known, but the other two had never been discovered. Experts say no hacker would waste Zero Days in that manner.

–After penetrating the Windows 7 operating system, the code then targeted the “frequency converters” that ran the centrifuges. To do that it used specifications from the manufacturers of the converters. One was Vacon, a Finnish Company, and the other Fararo Paya, an Iranian company. What surprises experts at this step is that the Iranian company was so secret that not even the IAEA knew about it…

One additional impact that can be attributed to the worm, according to David Albright of the Center for Strategic and International Studies, is that “the lives of the scientists working in the facility have become a living hell because of counter-intelligence agents brought into the plant” to battle the breach. Ironically, even after its discovery, the worm has succeeded in slowing down Iran’s reputed effort to build an atomic weapon. And Langer says that the efforts by the Iranians to cleanse Stuxnet from their system “will probably take another year to complete,” and during that time the plant will not be able to function anywhere normally…

Speculation on the worm’s origin initially focused on hackers or even companies trying to disrupt competitors. But as engineers tore apart the virus they learned not only the depth of the code, its complex targeting mechanism, (despite infecting more than 100,000 computers it has only done damage at Natanz,) the enormous amount of work that went into it—Microsoft estimated that it consumed 10,000 man days of labor– and about what the worm knew, the clues narrowed the number of players that have the capabilities to create it to a handful.