"We have not seen this scale of attack, the aggressiveness and penetration, in the U.S. before," one researcher said.

Two prominent international law experts think the recent malware worm, if actually tied to Russia, constitutes a violation of the Geneva convention.

Poroshenko claimed to "have evidence that a recent cyber attack was also organized by the Russian Federation."

M.E. Doc, the company at the center of an international ransomware outbreak, was reportedly warned about insufficient digital security multiple times, and new evidence shows it had already been compromised by hackers before last week's incident.

Four days after its networks were infected, operations are still hamstrung at the pharmaceutical giant. U.S. employees have been reduced to keeping paper records of their work.

The hacking group has suspected ties to Russia and a history of launching destructive computer viruses, according to research conducted by Czech cybersecurity firm ESET.