Stuxnet, the world's first known cyber missile," was designed to sabotage special power supplies used almost exclusively in nuclear fuel-refining centrifuge systems, researchers studying its code have revealed. The discovery is another puzzle piece experts say points to Iran's nuclear centrifuge plants as the likely target. While the discovery may seem just another bit of circumstantial evidence, it is a critical one that appears to all but answer a central mystery surrounding Stuxnet: What was its target? Stuxnet was discovered in June by a Belarus antivirus company, and its unique ability to control industrial processes was uncovered by US researchers in July. But its true role as the world's first publicly known cyber super weapon - designed to cross the digital divide and destroy a very specific target in the real world - was only revealed in September. It now appears that a smoking gun within Stuxnet's software code targets power supplies almost certainly used inside any Iranian nuclear fuel refining plant, researchers say. Working separately, researchers at California computer security firm Symantec arrived at the same conclusion as researchers in Germany late last week: Nuclear-fuel centrifuges were the target. All of the circumstantial evidence points in the same direction: Natanz.