(Bloomberg) – The U.S. electric grid “faces imminentdanger” from cyberattacks, which are growing more frequent andsophisticated, according to the Energy Department.

In the department's landmark Quadrennial Energy Review, it warned that a widespreadpower outage caused by a cyberattack could undermine “criticaldefense infrastructure” as well as much of the economy and place atrisk the health and safety of millions of citizens.

“Cyber threats to the electricity system are increasing insophistication, magnitude, and frequency,” it said in the 494-pagereport. “The current cybersecurity landscape ischaracterized by rapidly evolving threats and vulnerabilities,juxtaposed against the slower-moving deployment of defensemeasures.”

76 recommendations

The department detailed 76 recommendations to boost energy,including increasing the collection of data about online breachesfrom utilities. Separately, it called for extending tax credits toboost construction of new nuclear reactors. Overall, the reportsaid, total investment requirements necessary for gridmodernization range from $350 billion to $500 billion.

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While the report noted cyber-attacks “have had limitedconsequences to date,” it said that a 2015 attack on the Ukrainiangrid that caused widespread power outages, “should be seen as anindicator of what is possible.”

Modified or new grid reliability requirements and increased datacollection on cyber-attacks, were other recommendations. The reportalso called for a new Energy Department assessment of cybersecurityfor natural gas pipelines.

The Quadrennial Energy Review is part two of a broadadministration-wide review of the nation's energy policies. Thefirst report, released in 2015 focusing on energy infrastructure,recommended spending $15.2 billion over a decade to improve thegrid, and called for $2 billion to upgrade the Strategic PetroleumReserve.

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