Microsoft recently warned one of the main advisory firms for the election campaign of Democratic candidate Joe Biden against being targeted by suspected state-backed Russian hackers, according to a Reuters report.

The sources said that the hacking attempts over the past two months have targeted employees of Washington-based SKDKnickerbocker, a campaign management company that works with Biden and other prominent Democrats.

A source familiar with the matter told Reuters that SKDK's response to the information about the hacking attempt was to confirm that the hackers had failed to gain access to the company's networks.

"They are well protected, so there was no breach," the source person said.

Microsoft has identified the hackers as hackers supported by the Russian state (Reuters)

SKDK Vice President Hillary Rosen declined to comment to Reuters.

A Biden spokesman did not respond to a request for comment.

The hacking attempts on SKDK come as US intelligence agencies have raised concerns about potential efforts by foreign governments to interfere in the presidential elections next November.

Investigations by former special counsel Robert Mueller and the Senate Intelligence Committee concluded that those affiliated with the Russian government interfered in the 2016 presidential election, and Mueller warned that Russia might interfere in the current campaign.

One of the sources said it was not clear if the Biden campaign was the target or whether the Russians were trying to gain access to information about other SKDK clients.

Anita Dunn, executive director at SKDK, served as the White House communications director during Barack Obama's presidency and as a counselor on the Biden campaign.

Microsoft, which recently revealed the attempts, has identified the possible perpetrators as hackers supported by the Russian state, according to Reuters.

The three sources said that the attacks included phishing, a hacking method that seeks to trick users into revealing passwords, as well as other efforts to breach the SKDK network.

Closely associated with the Democratic Party, SKDK has served in six presidential campaigns and several congressional races.

In addition to her current job for Biden, the company has also worked in 2018 on successful campaigns for referees in Kansas and Connecticut.