A respected American computer science professor claims the US election may well have been hacked, and has urged Hillary Clinton to demand a recount.

On Thursday (AEST), Democratic candidate and election loser Mrs Clinton was leading President-elect Donald Trump in the popular vote by an unprecedented 1.82 million votes.

But Professor J. Alex Halderman, director of the University of Michigan Center for Computer Security and Society, argued in a Medium post that wildly contradictory pre-polling could possibly be due to the electoral system being compromised by Russia or another nation.

“A few years ago, I might have said that sounds like science fiction, but 2016 has seen unprecedented cyberattacks aimed at interfering with the election,” Professor Halderman wrote, arguing that Mrs Clinton had performed suspiciously poorly in some counties that required electronic voting rather than paper ballots.

President Barack Obama and President-elect Donald Trump shake hands. Photo: Getty

“The only way to know whether a cyberattack changed the result is to closely examine the available physical evidence ,” he wrote.

The professor’s plea is time sensitive, as Mrs Clinton would have to lodge an application (at her own expense) for a recount by next Wednesday.

‘Russia has shown a willingness to hack elections’

Professor Halderman said that while it was likely the pre-polling was “systematically wrong”, it was incumbent on Mrs Clinton to call for recounts in the marginal swing states.

He outlined the evidence suggesting Russia might just be brazen enough to carry out such an attack, including how attackers broke into the email system of the Democratic National Committee, into the email account of Mrs Clinton’s campaign chairman John Podesta, and infiltrated the voter registration systems of two states, Illinois and Arizona, stealing voter data.

“And there’s evidence that hackers attempted to breach election offices in several other states,” Professor Halderman wrote.

While pointing to Russia as a nation with the “sophisticated cyber-offensive capabilities” to exercise such a large-scale attack, he noted that a number of other countries were also capable.

Finally, the professor criticised paperless voting as vulnerable to hackers.

In the US, different counties and states use different voting systems.

Paper ballots are the only way to prevent against hackers, he said. Photo: CNN

California banned computer voting in 2007, while a number of states, including Louisiana, Georgia and South Carolina, continue to use them.

Other states use paper ballots, or machines that create a paper vote that cannot then be hacked by external forces.

For a computer scientist, Professor Halderman’s preference was interesting.

“Paper ballots are the best available technology for casting votes,” he wrote.

Clinton performed badly in ‘Rust Belt’ states

The first US candidate to lose the presidential election despite winning the popular vote, Mrs Clinton failed to perform in a trio of must-win states referred to as the Rust Belt.

These were Michigan (where Professor Halderman is based), Pennsylvania and Wisconsin.

Hillary Clinton will regret not campaigning in Wisconsin. Photo: Getty

Mr Trump won Wisconsin and Pennsylvania, with Michigan incredibly still too close to call weeks after election day.

The states represent a sizeable 46 electoral college votes between them (Mrs Clinton currently trails Mr Trump by 58).

Currently, Mrs Clinton trails by just 0.3 per cent in Michigan, 0.7 per cent in Wisconsin and 1.2 per cent in Pennsylvania.

High on her list of campaign mistakes was neglecting to visit Wisconsin, but based on pre-polls you might not blame her.

The formerly safe Democrat state had Mrs Clinton ahead by 6.5 points at the time of the election, and had never put Mr Trump in with a chance.