Microsoft Corp. says malicious hackers from Russia, Iran and China have repeatedly tried - but failed - to steal data from people and organizations involved in the U.S. presidential election set for Nov. 3.

Microsoft said Russian state-sponsored hackers, the most active, have targeted the campaign of Democratic Party presidential candidate Joe Biden.

It said Russian hackers had hit more than 200 organizations, most of which are "directly or indirectly affiliated with the upcoming U.S. election as well as political and policy-related organizations in Europe." The Russians seem to be attacking mostly Democrats, but are known to have tried to hack into a few Republican Party networks, too.

Foreign interference was confirmed by top officials of the U.S. intelligence community who said they had uncovered evidence Russia was currently interfering in the election to hurt the Biden campaign.

They also said China and Iran preferred President Donald Trump be defeated, but China hackers weren't interfering with Trump as much as Russia was with Biden. Microsoft said China hackers had also targeted Biden's campaign - but only intermittently.

Microsoft has warned one of Biden's main election campaign advisory companies it was being infiltrated by Russian hackers. It said for the past two months, Russian hackers had been attacking SKDKnickerbocker (SKDK), a campaign strategy and communications company working with Biden. It said the attacks on SKDK included phishing and other efforts to infiltrate the organization's network.

Microsoft said the same Russian hacking groups going after SKDK were those identified by U.S. law enforcement agencies as being responsible for the attacks on Hillary Clinton's presidential campaign in 2016.

It said the Russian tactics had evolved since 2016 and included automated and relentless "brute force" attacks on computer networks.

On the other hand, Iran hackers are paying special attention to the Trump campaign. Microsoft said that from May to June of this year, Iran hackers tried to log in to the accounts of Trump administration officials and Trump campaign staff.

"What we've seen is consistent with previous attack patterns that not only target candidates and campaign staffers but also those who they consult on key issues," Microsoft said.

Top government cybersecurity officials confirmed Microsoft detected attempts to infiltrate email accounts of people and organizations associated with the presidential race. None of the attacks seems to have been directed against vulnerable voting infrastructure, however.

"It is important to highlight that none (of those hit) are involved in maintaining or operating voting infrastructure and there was no identified impact on election systems," said Chris Krebs, director of the Department of Homeland Security's Cybersecurity and Infrastructure Security Agency.

"We encourage anyone that experiences a cyber-incident to report to CISA and the FBI."