NEW YORK (NYTIMES) - Fifty-nine of the country's top computer scientists and election security experts rebuked US President Donald Trump's baseless claims of voter fraud and hacking on Monday (Nov 16), writing that such assertions are "unsubstantiated or are technically incoherent."

The rebuttal, in a letter to be published on various websites, did not mention Mr Trump by name but amounted to another forceful corrective to the torrents of disinformation that he has posted on Twitter.

"Anyone asserting that a US election was 'rigged' is making an extraordinary claim, one that must be supported by persuasive and verifiable evidence," the scientists wrote. In the absence of evidence, they added, it is "simply speculation."

"To our collective knowledge, no credible evidence has been put forth that supports a conclusion that the 2020 election outcome in any state has been altered through technical compromise," they wrote.

The letter followed a similarly strong rebuttal of the president's claims last week by the Elections Infrastructure Government Coordinating Council, which includes top officials from the Department of Homeland Security's cybersecurity agency, the US Election Assistance Commission, and secretaries of state and state election directors from around the country.

In a joint statement on Thursday, that group declared that the 2020 election "was the most secure in American history" and that "there is no evidence" any voting systems had been compromised. Some of those officials expect to be fired in the coming weeks for their refusal to echo the president's claims.

Over the past week, Mr Trump has tweeted various conspiracy theories involving Dominion, a major supplier of voting machines and other election technology. Among them, Mr Trump wrote that Dominion machines had "deleted 2.7 million Trump votes nationwide," a claim with no basis in fact.

Of five counties that experienced different software problems on Election Day in Michigan and Georgia, only two used Dominion software, and in each case the problems were fixed and did not affect results.

Over the weekend, Mr Trump also shared a video clip taken last year at the annual DefCon hacking conference in Las Vegas, where hackers probe voting machines sold by Dominion and Elections Systems & Software, looking for ways to manipulate the vote. The effort was meant to draw awareness to election security, and there is no evidence that the machines have ever been manipulated in an election.

"We have never claimed that technical vulnerabilities have actually been exploited to alter the outcome of any US election," the election security experts wrote in their statement Monday.

For years, election integrity and digital security specialists have called for improved security on voting machines and other election technical infrastructure, to add greater transparency and postelection auditing procedures.

They were largely rebuffed at the federal level. The Senate majority leader, Mr Mitch McConnell, killed three election security measures last year, arguing that they were unnecessary and "partisan."

Last year, one day after Mr Robert Mueller, the former special counsel, testified that Russia was trying to sabotage the 2020 election, Mr McConnell made clear that he was not going to pass election security legislation.

"Clearly something so partisan that it only received one single solitary Republican vote in the House is not going to travel through the Senate by unanimous consent," Mr McConnell said on the Senate floor in July 2019.

Now Mr Trump and other Republicans have called for some of the same measures, like risk-limiting audits, that Mr McConnell blocked. Those Republicans include Mr Rand Paul, Mr McConnell's fellow senator for Kentucky.

"I wrote, and the House passed, the toughest election security reform Bill to date, which then died in the Senate at Mitch McConnell's hands," Senator Ron Wyden said in an email. "It takes a special kind of chutzpah to block every single Bill to make our elections more secure and then question the legitimacy of this election."

That inaction, coupled with the unfounded claims against the election technology companies, has exasperated researchers.

"It has been extremely frustrating that the existence of serious vulnerabilities is now being confused with the actual exploitation to tamper with elections, which is something that we've never seen any evidence for," said Professor Matt Blaze, a computer science expert from Georgetown University who signed the letter.

The group has persuaded some states to strengthen security. It helped get Colorado to put in place rigorous audits that examine samples of ballots for evidence of incorrect tallying, for example, but has been unsuccessful in pushing those measures at the federal level.

Other signers of the letter include Prof Ronald Rivest from the Massachusetts Institute of Technology and a pioneer in cryptography; Prof Steven Bellovin, a computer science expert at Columbia University; Mr Joseph Lorenzo Hall, the senior vice-president at the nonprofit Internet Society; Mr J. Alex Halderman, an election security expert; and Mr Harri Hursti, an election security expert who was in Georgia during the election.