Report ponders what follows a cyber attack on electric grid.

• Position: Homeland Security News

Experts are convinced that a cyber attack on a U.S. electric grid that could cut off power to millions is a near certainty.

The question is, what comes next? A report by the Bipartisan Policy Center, "Cybersecurity and the North American Electric Grid: New Policy Approaches to Address an Evolving Threat," devoted a chapter to what authorities may need to do in the event that a terrorist group, nation state or insider successfully switches off electricity in a major U.S. city.

"In the early phases [of the attack], it may not be possible to identify either the origins of an attack or its implications for the broader system," said the report.

The example experts cite most often had nothing to do with terrorism. The 2003 multiday blackout in the Northeast that affected some 55 million customers in the United States and Canada was caused by a software bug in an Ohio control room and some unpruned trees. But it took almost a year for investigators to find out exactly what happened.

"Ten years ago we would have this conversation and say, 'What if?' Today ... I think the question is, 'When?'" Curt Hebert, former chair of the Federal Energy Regulatory Commission, and co-chair of the committee that wrote the report, said of a cyber attack on a grid.

More recently, Hurricane Sandy in 2012 pointed out further shortcomings in power delivery recovery efforts. Since then, utilities and other companies with grid assets have been working to strengthen their recovery plans, the report said.

"That said, the disruptions associated with a large-scale cyber attack are likely to challenge utilities' operational abilities," the report said.

There are two frameworks in place that are intended to guide federal...