Former US cybersecurity chief Chris Krebs says officials are still tracking 'scope' of the SolarWinds hack

• Chris Krebs, the former head of the Cybersecurity and Infrastructure Security Agency, said on Sunday the massive SolarWinds cybersecurity attack appears to be linked to Russia.
• "Everything I've heard, whether it's from private sector cybersecurity threat and intelligence experts, things I have heard out of Congress – it's Russia," Krebs said on CNN's "State of The Union" Sunday.
• Krebs warned that the scale of the cybersecurity breach was "probably more broad" than the hacking of SolarWinds, but said he would "be very careful about escalating" when asked if the US should retaliate.

Chris Krebs, former head of the Cybersecurity and Infrastructure Security Agency, said the massive SolarWinds cybersecurity attack appears to be linked to Russia, but the US should be cautious in its response.

Cybersecurity researchers said last week that from as early as March, hackers compromised software company SolarWinds' system to spy on its clients, Business Insider's Aaron Holmes previously reported. The company's customers include key government agencies such as the White House, the Pentagon, and the US Treasury Department.

"Everything I've heard, whether it's from private sector cybersecurity threat and intelligence experts, things I have heard out of Congress - it's Russia," Krebs said on CNN's "State of The Union" on Sunday. "They're exceptionally good at this."

Secretary of State Mike Pompeo said on Friday that "we can say pretty clearly that it was the Russians that engaged in this activity," and as The Washington Post reported, others familiar with the matter have attributed the cybersecurity attacks to Russia as well. However, President Donald Trump on Saturday contradicted these statements and in a series of tweets, suggesting "the possibility that it may be China," Business Insider's John Dorman reported.

Krebs said the US is "just getting our arms around the scope of this cyber-compromise," and the scale of this breach is "probably more broad" than SolarWinds.

He also doubled down that the culprit behind the attacks was Russia, adding: "the Russian intelligence service, the SVR, they're really the best of the best out there."

However, when pressed by host Jake Tapper about whether the US should retaliate against Russia, Krebs cautioned he would "be very careful about escalating this."

"I think there needs to be a conversation globally, internationally across like-minded countries about what is acceptable," he added.

Krebs was fired from his role as the head of CISA last month not long after he publicly pushed back against Trump's baseless claims of voter fraud in the election, Business Insider's Sonam Sheth reported.

• Read more:
• 'It's not how I wanted to go out': Chris Krebs, the election security official fired by Trump, opens up in new interview and dismisses 'farcical' claims of voter fraud
• Why the impact of the unprecedented SolarWinds hack that hit federal agencies is 'gargantuan' and could hurt thousands of companies, according to cybersecurity experts
• How hackers breached IT company SolarWinds and staged an unprecedented attack that left US government agencies vulnerable for 9 months
• Trump contradicts Pompeo as he breaks his silence on SolarWinds cyberattack and shifts focus to China instead of Russia