Hackers linked to Russia, China and Iran are trying to spy on people tied to both United States President Donald Trump and Democratic challenger Joe Biden, Microsoft Corp said.
The report came amid revelations that one of Mr Biden's main campaign advisory firms had been warned by the American software giant that it was in the cross hairs of the same Russian hackers who intervened in the 2016 US election.
Microsoft's statement, released on Thursday, highlights how advisers to both campaigns are at risk from digital spies worldwide, as both candidates face off on Nov 3.
The announcement by Microsoft's VP for customer security Tom Burt said the group accused of breaching Mrs Hillary Clinton's campaign e-mails in 2016a Russian military intelligence-linked unit widely known as Fancy Bearhad spent the past year trying to break into accounts belonging to political consultants serving both Republicans and Democrats.
Mr Burt also said Chinese hackers had gone after people "closely associated with US presidential campaigns and candidates"including an unnamed ally of Mr Biden who was targeted through a personal e-mail address and "at least one prominent individual formerly associated with the Trump administration".
He added that Iranian hackerswhich Microsoft has already called out publicly for attempts to spy on a US political campaignhad since tried to log in to accounts belonging to Trump administration officials and members of the Republican President's campaign staff.
Microsoft's announcement was planned before news broke that Fancy Bear was suspected of targeting Washington-based SKDKnickerbocker, a campaign strategy and communications firm working with Mr Biden and other Democrats.
Mr Burt said the Chinese effort to compromise Mr Biden's ally and the Iranian spying against the Trump campaign were unsuccessful.
Speaking generally, he stated that foreign hacking was intensifying as the vote drew nearer.
"The activity we're announcing today makes clear that foreign activity groups have stepped up their efforts targeting the 2020 election as had been anticipated."
The Department of Homeland Security's top cyber official Christopher Krebs said Microsoft's warning was consistent with earlier statements issued by the intelligence community about Russian, Chinese, and Iranian spying on election-related targets.
"It's important to highlight that none are involved in maintaining or operating voting infrastructure and there was no identified impact on election systems," Mr Krebs said.
The Biden and Trump campaigns both said they were aware of the targeting and were not surprised by it.
Speaking at a joint press conference in Moscow with his Russian counterpart Sergei Lavrov, Chinese Foreign Minister Wang Yi said China has never meddled in US affairs. Mr Lavrov, in turn, said accusations of Russia using hackers to meddle in US internal affairs were "unsubstantiated".
Russian Embassy press secretary Nikolay Lakhonin said Americans had been discussing "so-called interference" for years without presenting what he described as "factual evidence".
China earlier in the day accused Microsoft of "fabrication" and "creating trouble". Its Foreign Ministry spokesman Zhao Lijian said the US was itself an "empire of hackers".
Mr Alireza Miryousefi, spokesman for Iran's United Nations mission in New York, said it was "preposterous to even think that Iran would conduct hacking".
It's not unusual for state-backed hackers to go after politicians in an election year.
Mr John Hultquist, an analyst at cyber-security company FireEye's Mandiant unit, said: "Parties and campaigns are good sources of intelligence on future policy."
But he added that he was particularly concerned by the news that Fancy Bear was active, saying the group history of leaking data it hacked "raises the prospect of follow-on information operations or other devastating activity".
REUTERS, AGENCE FRANCE-PRESSE