Stuxnet is a malicious computer worm believed to be a jointly built American-Israeli cyber weapon. Although neither state has confirmed this openly, anonymous US officials speaking to the Washington Post claimed the worm was developed during the Obama administration to sabotage Iran’s nuclear program with what would seem like a long series of unfortunate accidents.
Stuxnet specifically targets PLCs, which allow the automation of electromechanical processes such as those used to control machinery on factory assembly lines, amusement rides, or centrifuges for separating nuclear material. Exploiting four zero-day flaws, Stuxnet functions by targeting machines using the Microsoft Windowsoperating system and networks, then seeking out Siemens Step7 software. Stuxnet reportedly compromised Iranian PLCs, collecting information on industrial systems and causing the fast-spinning centrifuges to tear themselves apart. Stuxnet’s design and architecture are not domain-specific and it could be tailored as a platform for attacking modern SCADA and PLC systems (e.g., in automobile or power plants), the majority of which reside in Europe, Japan and the US. Stuxnet reportedly ruined almost one-fifth of Iran's nuclear centrifuges.
Stuxnet has three modules: a worm that executes all routines related to the main payload of the attack; a link file that automatically executes the propagated copies of the worm; and a rootkit component responsible for hiding all malicious files and processes, preventing detection of the presence of Stuxnet.
Stuxnet is typically introduced to the target environment via an infected USB flash drive. The worm then propagates across the network, scanning for Siemens Step7 software on computers controlling a PLC. In the absence of either criterion, Stuxnet becomes dormant inside the computer. If both the conditions are fulfilled, Stuxnet introduces the infected rootkit onto the PLC and Step7 software, modifying the codes and giving unexpected commands to the PLC while returning a loop of normal operations system values feedback to the users.
In 2015, Kaspersky Labs' research findings on another highly sophisticated espionage platform created by what they called the Equation Group, noted that the group had used two of the same zero-day attacks used by Stuxnet, before they were used in Stuxnet, and their use in both programs was similar. The researchers reported that "the similar type of usage of both exploits together in different computer worms, at around the same time, indicates that the EQUATION group and the Stuxnet developers are either the same or working closely together".