Senior intelligence officials are warning the Western world that Russia's interference in the 2016 US election was an escalation of aggression that is likely to continue.

Robert Hannigan, the former head of UK signals intelligence service GCHQ, has told Four Corners further attacks from Vladimir Putin are probable.

"As long as Putin can't address Russian economic problems, he's probably going to be tempted to wrap himself in the flag of nationalism even more firmly and to do more foreign adventures. I hope not, but I fear that might be the case," he said.

Dan Hoffman, former CIA station chief in Moscow, says this new threat from Russia should not be underestimated.

"As dangerous as things were between our countries during the Cold War, as much risk as there was of conflict, you might argue that we're in a worse place today," he told Four Corners.

Former CIA Moscow station chief Dan Hoffman issues a warning to the Western world.

Mr Hoffman's scrutiny of Russian actions during the 2016 election campaign has led him to conclude that sophisticated spycraft was at play.

He points to the infamous 2016 Trump Tower meeting, which he says was a deliberately discoverable Russian operation.

"I think what Vladimir Putin was thinking is the best way to soil our Democratic processes, link the Trump campaign in some conspiratorial way, because it's Russia, back to the Kremlin."

Two years on from that meeting, President Donald Trump and his team are still being investigated over allegations of Russian collusion.

Mr Hoffman told Four Corners this chaos was Mr Putin's plan all along.

In June 2016, senior members of Mr Trump's election campaign team including the President's son Don Junior and son-in-law Jared Kushner, agreed to meet with several Russians in Trump Tower.

They had been promised they would receive "incriminating information" about then-presidential rival Hillary Clinton.

James Clapper, Barack Obama's director of national intelligence, told Four Corners the Trump team's willingness to work with the Russians is telling.

"What it reflects is an interest in collusion, whether anything came of it that's yet to be determined, but I do wonder whether that's just one vignette that became public and were there other such encounters? I don't know," he said.

At the June 9 meeting, Russian lawyer Natalia Veselnitskaya gave the Trump team a memo which included unproven allegations of wrongdoing by donors to Hillary Clinton's campaign.

This was far from the explosive information that had been promised.

Ms Veselnitskaya told Four Corners she was meeting with the Trump team on private business for a client.

But she had discussed the information with Yuri Chaika, the general prosecutor of Russia and one of the most powerful figures in the Putin regime.

"I personally reported this to Mr Chaika, I don't know exactly, but many, many months before this meeting," she told Four Corners.

Sorry, this video has expired 'Are you a spy for the Russian Government?' Natalia Veselnitskaya says of course not.

'It was meant to be found'

Mr Hoffman says the Trump Tower meeting has the Russian President's fingerprints all over it.

"It wasn't meant to be a clandestine operation, that's the last place he would ever do that. There's too much security, too much press, too many people there," he said.

"What I think Vladimir Putin was doing, was deliberately leaving a trail of breadcrumbs from Trump Tower to the Kremlin.

"I see the full spectrum of Russian intelligence operations and frankly, if the media can find something that Russia did, like the meeting at Trump Tower, then it was meant to be found."

Since the news of the meeting broke in the US media last year, Ms Veselnitskaya has been fending off accusations she is a Russian spy.

She told Four Corners she was not a Russian operative and rejected the idea there was any "collusion" involved in the meeting.

"Give me the motive. Explain why? Why on earth would the Kremlin do that? What on earth would they be talking about with Trump? And more importantly what could Russia have done to help Trump win?" Ms Veselnitskaya said.

Mr Hoffman believes Mr Putin's intention was to spark a media frenzy.

"[It was] kind of like a poison pill. Eventually the media will expose them," he said.

"He's playing chess, he's thinking a few moves ahead and he doesn't always let his pawns know exactly what his strategy is to tip over our king. That's what he was doing with these people.

"It wasn't that they even did anything again, particularly sinister at all. In fact, far from it.

"What was sinister is that they were there to soil the Trump campaign and by extension, our democratic process, that's it."

Dan Hoffman believes Vladimir Putin was 'deliberately leaving a trail of breadcrumbs from Trump Tower to the Kremlin'. ( Reuters: Aleksey Nikolskyi/Kremlin )

Mr Putin's covert war against America during the 2016 election was also waged online.

Russia used sophisticated cyber units from within its own intelligence services, as well as the privately owned Internet Research Agency.

It was a coordinated digital assault involving everything from subtle social media manipulation to outright cyber-attacks and theft.

Mr Hannigan said what concerned him most about this operation was Russia's overt aggression.

"What's particularly striking is they don't seem to mind being called out, or having it attributed to them, so, that is a big change," he said.

"They've always been gathering intelligence and getting themselves positioned. What we've seen in the last four or five years in a whole range of countries, is a willingness to do destructive and often reckless things."

WikiLeaks and the hacked emails

Russia's biggest cyber coup during the US election was the attack on the servers of the Democratic National Committee and the personal email account of campaign chairman John Podesta.

Material from these hacks was later published online by WikiLeaks.

Whether the Trump team knew in advance about these hacks, is at the heart of special prosecutor Robert Mueller's investigation into Mr Trump, his family and associates.

Mr Hannigan doesn't believe Mr Putin was aiming for Mr Trump to win in 2016.

"I think the objective was not a grand strategy to get a particular person elected," he said.

"I think the objective was pretty much what the Russian Intelligence Services have always tried to do, which is to disrupt Western democratic institutions.

"To sow distrust in the public and to undermine confidence in democracy."

Mr Clapper told Four Corners he has no doubt of Mr Putin's authorship of this campaign against America.

"To sow discord and discontent and doubt about our system and they succeeded fairly well in doing that. They played to the schisms, to the polarisation, played to the interest of our various tribes," he said.

Mr Hoffman agrees.

"Vladimir Putin realised he could inject this virus into our political system and set us fighting against each other instead of remembering that the enemy is not Google, Facebook, Twitter, Democrats, Republicans — it's the guy in the Kremlin," he said.

Vladimir Putin gives his speech at the World Cup opening ceremony in Moscow. ( AP: Alexei Druzhinin )

With Russia hosting the World Cup, Mr Putin has just welcomed the world to a, "splendid football festival in a hospitable and friendly country", but intelligence officials observe a darker intent in Mr Putin's world view.

Mr Clapper told Four Corners the US's recent experiences with Russia should serve as a lesson for Australia.

"I've seen a lot of bad stuff in 50 years in intelligence, but [it was] just viscerally disturbing that an adversary country was so aggressively meddling in our political process," he said.

"I think in your case, [it's] the Chinese and the extent to which China involves itself in your political process in seeking to gain political influence. I don't think there's a magnitude of that in Australia that we've experienced here, but I think it's a danger."

Watch part three of the Four Corners Trump/Russia investigation — Moscow Rules — at 8.30pm on ABC TV and ABC iview.