He said Britain's critical infrastructure was vulnerable to disruption at sites where industrial control systems were linked to the internet.

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For example, industrial control systems are largely computer controlled and they can be reached in some cases from the Internet.

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Unlike Stuxnet, which specifically damaged Siemens PCS 7 systems, Duqu appears to be only collecting information about the design of other industrial control systems.

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The virus penetrated the Iranian systems through Siemens industrial control systems.

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That has left industrial control systems vulnerable to attack.

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Symantec observed virtually no targeted attacks before Stuxnet, a worm that attacked industrial-control systems, appeared in 2010.

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What is clear is that critical infrastructure and industrial plant control systems are coming under more scrutiny from both attackers and defenders.

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One of the key businesses of United Technologies is also in the area of climate control systems and services for multifamily, commercial and industrial facilities.

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The sorts of computer systems it enters are those that control critical infrastructures like power plants, refineries and other industrial targets.

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