This is scary.

The Wall Street Journal's Rebecca Smith reports that a former Federal Energy Regulatory Commission chairman is acknowledging for the first time that a group of snipers shot up a Silicon Valley substation for 19 minutes last year, knocking out 17 transformers before slipping away into the night.

The attack was "the most significant incident of domestic terrorism involving the grid that has ever occurred" in the U.S., Jon Wellinghoff, who was chairman of the Federal Energy Regulatory Commission at the time, told Smith.

A blackout was avoided thanks to quick-thinking utility workers, who rerouted power around the site and asked power plants in Silicon Valley to produce more electricity. But the substation was knocked out for a month.

The FBI says it doesn't believe a terrorist organization caused the attack but that it continues to investigate the incident.

Smith and colleague Tom McGinty assembled a detailed chronology of the attack that includes some amazing details, including more than 100 fingerprint-free shell casings similar to ones used by AK-47s that were found at the site and small piles of rocks that appeared to have been left by an advance scout to tell the attackers where to get the best shots.

A U.S. Navy investigation ordered by Wellinghoff determined "it was a targeting package just like they would put together for an attack," he said.

Other utility officials disagree with Wellinghoff's assessment, and say the electric grid remains highly resilient.

Click here to read the full story at WSJ.com »