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8. Stuxnet (2010)
The most sophisticated malware observed, this is a uniquely targeted worm that propagates via Windows and attacks industrial controller hardware — but only of a certain configuration (such as the Siemens S7-300 controller, above).
It is thought to have been designed to damage the Iranian nuclear programme, and may well have succeeded. When it finds its target system, it reprograms high-frequency motor controllers to operate in an intermittently out-of-specification way. It thereby upsets industrial processes in a manner that's hard to identify.
Although the authors of Stuxnet aren't known, reports earlier this year said that the malware was claimed as a success of the Israeli Defence Force, in a video shown at the retirement party of the force's chief of general staff, Lieutenant General Gabi Ashkenaz.
Photo credit: Ulli1105