Over the last nine months, dozens of U.S. power companies were compromised by an organized hacking group to the extent that some of them could have sabotaged and shut down production and distribution, according to Symantec, a cybersecurity company that discovered the attack.

In some cases, this involved access to details about how the company operated, engineering plans and equipment, in some cases even down to the level of controlling valves, pipes or conveyer belts, said Vikram Thakur, principal research manager at Symantec, which discovered the intrusions and first published information about them in a blog posting Wednesday.

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