Stuxnet - General Information via Wikipedia.

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Stuxnet is a malicious computer worm, first identified in 2010 but thought to have been in development since at least 2005, that targets industrial computer systems and was responsible for causing substantial damage to Iran's nuclear program. Although neither country has admitted responsibility, since 2012 the worm is frequently described as a jointly built American-Israeli cyberweapon.^[1][2]

Stuxnet specifically targets programmable logic controllers (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,^[3] Stuxnet functions by targeting machines using the Microsoft Windows operating 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.^[4] Stuxnet’s design and architecture are not domain-specific and it could be tailored as a platform for attacking modern supervisory control and data acquisition (SCADA) and PLC systems (e.g., in factory assembly lines or power plants), the majority of which reside in Europe, Japan and the US.^[5] Stuxnet reportedly ruined almost one fifth of Iran's nuclear centrifuges.^[6] Targeting industrial control systems, the worm infected over 200,000 computers and caused 1,000 machines to physically degrade.^[7]

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.^[8] It 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.^[9][10]

In 2015, Kaspersky Labs noted that the Equation Group had used two of the same zero-day attacks, prior to their use in Stuxnet, and commented 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".^[11]