An online “impersonator” of a Democratic National Committee (DNC) staffer tried to contact presidential campaigns, including Sen. Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE’s (I-Vt.) campaign, the committee said in a statement to the candidates Wednesday.

Bob Lord, the DNC’s chief security officer, wrote in an email to the campaigns obtained by The Hill that “adversaries will often try to impersonate real people on a campaign."

He added that the “adversaries” could try to get campaign workers to “download suspicious files, or click on a link to a phishing site” or set up calls or in-person meetings to record and release.

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Lord warned that the “impersonator” contacted the Sanders campaign and at least two others and had a domain registered overseas. But he acknowledged that anyone can register a domain name in any country.

“Attribution is notoriously hard,” he wrote. “The appropriate authorities have been alerted.”

“If you are using an alternate domain, please refrain from doing so and let us know if you are operating from a domain that others have not corresponded with before,” Lord added. “Do not use your personal mail account for official business.”

Sanders campaign spokesman Mike Casca confirmed the incident with The Associated Press and said the domain was registered in Russia.

“It’s clear the efforts and investments made by the DNC and all the campaigns to shore up our cybersecurity systems are working,” Casca said, according to the AP. “We will remain vigilant and continue to learn from each incident.”

The Hill reached out to the DNC and the Sanders campaign for confirmation.

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The Vermont senator said on Friday that he was briefed about a month ago that Russia was attempting to boost support for his presidential campaign.

Democratic campaigns have been cautious about cybersecurity since John Podesta’s emails were hacked and published after the Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE campaign chairman received an email seemingly from Google directing him to change his account.

--This report was updated at 12:17 p.m.