"Russia is one of the two most capable cyber adversaries we face globally: They are a formidable foe," Vorndran said on Tuesday. "The threat from Russia in the criminal sense and the nation sense is very real - and current."
When asked by a congressman whether Russia could win a war directly through cyber attacks that paralyzed US defense and other capabilities, Vorndran avoided giving any direct answer to the question.
"Can Russia win a war with cyber attacks? That's a really hard question for me to answer," Vorndran said.
State-sponsored hacking from Russia posed a "current" threat to US national security, he added.