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Hillary Clinton and Donald Trump have gone toe-to-toe on cyber security, with both presidential candidates warning that the stakes are high in the next age of digital warfare.

But what's the biggest threat to America's national cybersecurity? Well, that depends who you ask.

During Monday night's first presidential debate, in a segment called "Securing America," Democratic nominee Hillary Clinton described cyber security and cyber warfare as "one of the biggest challenges facing the next president."

America's adversaries, according to Clinton, come in two guises. There are the "independent hacking groups" that attack the United States for commercial reasons, and then there are the "state actors" from overseas. Chief among them? Russia

"There's no doubt now that Russia has used cyber attacks against all kinds of organisations in our country and I'm deeply concerned about this," Clinton said.

"[Vladimir Putin has] let loose cyber attackers to hack in to Government files, to hack into personal files, hack into the Democratic National Committee, and we recently have learned that this is one of their preferred methods of trying to wreak havoc and collect information."

But Donald Trump was quick to dismiss Clinton's Russian hacking claims, proposing a much less glamorous alternative.

"I don't think anybody knows it was Russia that broke into the DNC," the Republican nominee said. "She's saying Russia, Russia, Russia. Maybe it was. It could be Russia but it could be China, it could be lots of people. It could be somebody that sits on their bed that weighs 400 pounds. You don't know who broke into DNC."

But the two candidates weren't totally opposed on cybersecurity.

"As far as the cyber, I agree to parts of what Secretary Clinton said," Trump said in response to his Democratic opponent.

The internet, and "the cyber", were quick to respond.

When it comes to presidential debates, never raise the wrath of cyber space.