Hackers stole data belonging to multiple electric utilities in an October ransomware attack on a US government contractor that handles critical infrastructure projects across the country, according to a memo describing the hack obtained by CNN.Federal officials have closely monitored the incident for any potential broader impact on the US power sector while private investigators have combed the dark web for the stolen data, according to the memo sent this month to power company executives by the North American grid regulator’s cyberthreat sharing center.The previously unreported incident is a window into how ransomware attacks on critical US companies are handled behind the scenes as lawyers and federal investigators quietly spring into action to determine the extent of the damage.The ransomware attack hit Chicago-based Sargent & Lundy, an engineering firm that has designed more than 900 power stations and thousands of miles of power systems and that holds sensitive data on those projects.But security experts have long been concerned that schematics held by electric and nuclear power contractors could be dumped online and used for follow-on physical or cyberattacks on those facilities."