Washington (CNN) Russian intelligence operatives attempted to hack into the online accounts of staffers on three congressional campaigns in the upcoming midterm elections, a Microsoft executive said Thursday, marking the first public acknowledgment of a Russian attack on a 2018 race.

Speaking at the Aspen Security Forum, Tom Burt, Microsoft's corporate vice president for customer security and trust, said the technology firm had earlier this year detected a fake domain that was likely used as part of phishing attacks directed at the three campaigns.

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Microsoft took down the site and prevented the victims from "being infected by that particular attack," Burt said.

Multiple US intelligence and homeland security officials have said in recent days that Russia has not yet attempted a large-scale effort to manipulate specific election infrastructure in the midterm elections, as it did in the 2016 race.

Burt said the specific phishing tactic, which generally involves duping a victim into clicking a malicious link, was one they discovered being used by a Russian intelligence hacking group often referred to as Fancy Bear in the lead-up to the presidential election.

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