Stuxnet

From the Christian Science Monitor:

The cyber worm, called Stuxnet, has been the object of intense study since its detection in June. As more has become known about it, alarm about its capabilities and purpose have grown. Some top cyber security experts now say Stuxnet's arrival heralds something blindingly new: a cyber weapon created to cross from the digital realm to the physical world – to destroy something.
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The appearance of Stuxnet created a ripple of amazement among computer security experts. Too large, too encrypted, too complex to be immediately understood, it employed amazing new tricks, like taking control of a computer system without the user taking any action or clicking any button other than inserting an infected memory stick. Experts say it took a massive expenditure of time, money, and software engineering talent to identify and exploit such vulnerabilities in industrial control software systems.
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Stuxnet's ability to autonomously and without human assistance discriminate among industrial computer systems is telling. It means, says Langner, that it is looking for one specific place and time to attack one specific factory or power plant in the entire world.