The United States has spent $1 trillion on homeland defense since the world's worst terrorist attacks 12 years ago killed almost 3,000 peolple. Yet America is now more vulnerable than it was in 2001.

How is this possible?

The answer is a defenseless ether -- or cyberspace. And China is arguably the most aggressive nation in cyberspying. Beijing's global vacuum cleaner has cleaned America's clock, from defense firms to classified research labs to global corporations.

This gigantic operation was brilliantly illustrated by three top experts at a June 3 meeting of the Atlantic Council.

What Edward Snowden, the 30-year-old defector who handled top secret work for Booz Allen under a National Security Agency contract, purloined and made public by leaking it to Britain's liberal The Guardian and The Washington Post newspapers, paled next to China's electronic reach.

U.S. cyberexperts, who have worked in both the public (including top secret) and private sectors, are unanimous: "Advanced Persistent Threats," as China's clean sweep is known, "target every business."

Denials by China's Foreign Affairs Ministry are genuine. They aren't in their country's cyberspying loop. Nor is the U.S. State Department in Washington. But NSA topsiders are in awe over China's all-encompassing cyber intelligence loop.

"Without adequate investigation and without further evidence, accusing China of carrying out cyberattacks against U.S. companies is not only unprofessional but also irresponsible," said China's Foreign Ministry spokesman Hong Lei in an interview with CNBC.

Lei added China is the victim of cyber-theft attacks -- and "it's our duty to stop them anywhere they happen."

So it's a Mexican standoff. And there is no denying China is closing the technological gap with the United States in all key civilian and military research and development areas, from the banal to the most secret.

Beijing's forward planners now have access to company secrets and confidential strategies.

China, argue its many admirers in Western countries, is fearful of its slowest gross domestic product growth for the past 20 years. And its awesome cybertheft effort is the strategy for closing the gap.

Chinese leaders are also fearful of being left behind in the high-tech race that is an endless marathon.

China isn't alone in targeting the United States' vital organs. Other governments, including Russia's, as well as organized crime syndicates, and "hacker collectives," are busy trolling every facet of the U.S. economy.

Companies that get paid to protect corporate secrets are also high on China's list of priorities.

In a report to Congress, the Office of the National Counterintelligence Agency (under the CIA) described China's ether cleaner as "the world's most active and persistent perpetrators of economic espionage."

Not surprisingly, given Snowden's choice of destinations -- Hong Kong, Moscow, and possibly Ecuador (governed by a U.S.-hating president) -- the self-despised American defector only referred to U.S. activities in cyberspace. China's and Russia's cyberespionage was of little concern to him.

Snowden was clearly aided and abetted by WikiLeaks founder Julian Assange, who helped organize his global flight to elude U.S. prosecution.

Assange, cloistered at the Ecuadorian Embassy in London for the past year to evade a British arrest warrant (he's wanted for questioning in Sweden in relation to a sexual assault investigation), acted as Snowden's travel agent as he made his escape through countries where he felt safe (i.e., China and Russia).

Through the embassy's ground floor window, Assange hotly denied that Snowden was a traitor. The respectable synonym for traitor is now "whistleblower."

All the goodwill built up at the recent Sino-U.S. summit by President Barack Obama and Chinese President Xi Jinping seemed to vanish in a few hours as Beijing scuttled any chance of extradition proceedings.

White House spokesman Jay Carney said Obama thinks China pre-empted any chance of laying out the case that would have facilitated extradition.

In reality, Snowden was off to Moscow while Chinese leaders were debating what to do.

Neither Chinese nor Russian authorities made any move to detain him. In Moscow, he didn't leave the duty-free zone of the airport.

China's gigantic effort to raid America's corporate and defense secrets is now moving to the top of the Sino-American dialogue.

In the United States, some geostrategic experts are arguing for nuclear retaliation in response to major cyberattacks. Former counter-terrorism czar Richard Clarke, among other experts, say this should be off the table as it would be "destabilizing, dangerous and inimical to broader U.S. goals."

Clarke was responding to last January's Defense Science Board recommendation for countering "existential cyberattacks." In "The National Interest," rising GOP defense star Elbridge Colby makes the case for DSB.

"The (DSB) Task Force," he writes, "was saying that if an enemy hits us with a cyberattack of a scale comparable to a nuclear blow, we should be ready to retaliate with a nuclear strike. This is in line with longstanding U.S. nuclear doctrine, most recently restated in the 2010 Nuclear Posture Review, that the United States reserves the right to retaliate with nuclear weapons in response to non-nuclear attacks of great severity or danger -- in 'extreme circumstances,' in the Review's apt parlance."

"The U.S. needs deterrence," says Colby, "as we simply can't practically defend against large-scale, sophisticated cyber assaults. A central finding of the Task Force was that 'the full spectrum cyber threat (of a top-tier cyber power)' is of such magnitude and sophistication that it cannot be defended against ... a successful (Department of Defense) cyber strategy must include a deterrence component.'

"In other words," concludes Colby, "a military strategy relying only on defenses against cyberattacks is a recipe for failure."