Following a cyberattack in late December on a utility provider in the Ukraine that shuttered operations for 80,000 customers for six hours, the Electricity Information Sharing and Analysis Center (E-ISAC), a U.S. trade association, warned its members to improve their network defenses, according to a Reuters report.

A nine-page document released by the group remains confidential, though Reuters had a chance to review it, and reported that while it did not go so far as to name vulnerabilities in U.S. systems that could be open to attackers, the Ukraine incident is being cited as the first cyberattack to knock an electrical grid offline.

E-ISAC continues its investigation of the incident and said that – working with the federal government – it would provide more data.

BlackEnergy, malware that's been associated with the Russian hacking group Sandworm – already suspected of attacks on industrial control systems elsewhere, including the U.S. – was detected on the Ukraine plant's infected systems.