The U.S. government added three Russians and five companies said to be linked to Moscow's security forces.
As tensions ratcheted up between Russia and the West, NATO members were increasingly preparing for the worst.
Starting by targeting software in Ukraine, the ransomware NotPetya spread internationally, and the British government thinks the Russian military was behind it.
The hacking attack occurred last year, but the South Korean defense ministry has said little about it.
The hackers have obtained seven times more data than in the 2014 Sony security breach.
Government sites, banks, the postal service, Kiev's airport and the Chernobyl nuclear plant were all hit by the cyberattack.
The Air Force's 50th Wing requested information from defense contractors for help thwarting cyberattacks.
The company’s previous security breach exposed 1 billion users’ data.
Americans paid about $325 million in cyber ransom in 2015, and that figure will rise dramatically this year.
Defense Secretary Ash Carter says attacks designed to prevent Islamic State from commanding its forces.
U.S. cyber intelligence firm iSight Partners linked the incident to a Russian hacking group known as “Sandworm.”
A congressional advisory body says retaliating would make hacks more costly to perpetrators.
Director of National Intelligence James Clapper said his approach will be to "trust but verify."