It was the understanding of Mueller's office that the FBI believes a phishing attempt by Russian intelligence had been successful in at least one Florida county in the 2016 election, according to Mueller's report released Thursday.
The report said Mueller's office didn't independently verify the belief.
A spokeswoman in the FBI's Tampa office said Thursday that her office wasn't commenting.
In a statement, the Florida Department of State, which supervises Florida elections, said federal officials notified them in 2017 that Florida was unsuccessfully targeted by hackers in 2016.
"The Department maintains that the 2016 elections in Florida were not hacked," the statement said. "The Florida Voter Registration System was and remains secure, and official results or vote tallies were not changed. "
Then-U.S. Sen. Bill Nelson, a Democrat, said last August that Russians had penetrated the systems of certain Florida counties and had "free rein to move about" ahead of last year's midterm election.
After Nelson made his allegations, the Federal Bureau of Investigation and the Department of Homeland Security issued a joint letter saying that they saw no signs of any "new or ongoing compromises" of state or local election systems.
Then-Florida Gov. Rick Scott, a Republican who successfully ran against Nelson for his Senate seat last fall, seized on the letter to criticize Nelson, saying that the 76-year-old senator "has either been deeply confused or very dishonest - and an alarming possibility exists that he is both on this issue."
On Thursday, the president of the Florida State Association of Supervisors of Elections said he thought it was telling that Mueller's report referred only to a "Florida county government" and didn't specify an elections office.
"To me that's not indicative of breach of a county elections," said Paul Lux, supervisor of elections for Okaloosa County. "At the end of the day, most of what I've seen in Mueller report, as it relates in election results, is three-year old information that has already been reported."
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