New York (CNN) While Washington debates how damaging the Mueller report i s for President Donald Trump, there is no doubt about its verdict that Russia interfered in the 2016 presidential election in a "sweeping and systematic fashion."

The 448-page report provides new details on what was a coordinated and extensive Russian government effort to undermine the US electoral process.

Amongst the more striking revelations in the report are claims that Russian government hackers managed to compromise a Florida county's election systems and that Russia attempted to hack Hillary Clinton's campaign just five hours after Trump publicly appealed for her deleted emails.

Mueller claims Florida county was compromised

The report contains the first ever public US government claim that Russian hackers compromised a county's network in the leadup to the 2016 election, with an attack on an unnamed Florida county.

According to the report, "the FBI believes that this operation enabled the GRU to gain access to the network of at least one Florida county government."

Florida election officials were shocked by the claim.

"I have absolutely zero knowledge, per any briefing that I have sat in with the FBI, with Homeland Security, and I have sat in classified briefings as a part of my role on the Government Coordinating Council for Homeland Security," Chris Chambliss, the supervisor of elections in Clay County and the president of the Florida State Association of Supervisors of Elections during the 2016 elections, told CNN

"I have never heard any one of those agencies state that a Florida county was breached," Chambless added.

Dan McCrea -- who advises on Florida topics for Verified Voting, a voting integrity nonprofit -- told CNN that he and his local government contacts were all unaware of a county being compromised.

"Mueller knows more than any of the rest of us so we can assume the report is correct even if we don't know which county," McCrea said.

The GRU, Russia's military intelligence agency, is widely known to have made cursory attempts to influence the voting process in 2016, particularly in Florida. Previous reporting , public statements, and Mueller's 2018 indictment against GRU officers had already established that in the months leading up to the 2016 election, GRU officers had created Gmail accounts purporting to be from VR Systems, a Florida-based voter registration company.

At least a handful of Florida counties received such emails but they automatically were marked as spam. VR Systems itself eventually admitted one of its networks had been hacked.

Mueller's report reveals the GRU targeted "over 120 email accounts", more than the handful previously known about.

It is unclear which of Florida's 67 counties the report refers to. The FBI and Department of Homeland Security didn't immediately respond to questions on the topic.

Sarah Revell, a spokesperson for the Florida Department of State, said she didn't know either, but said her department had also reached out to the FBI.

"The Department maintains that the 2016 elections in Florida were not hacked. The Florida Voter Registration System was and remains secure, and official results or vote tallies were not changed," Revell said in a statement to CNN.

That reflects DHS' longstanding insistence that hackers didn't change any votes in 2016, though it's far more likely that a malicious actor that compromised a county network would make voting difficult, rather than actually change votes, as voting machines are kept offline.

Russia targeted Clinton emails hours after appeal from Trump

The report also provided new details on the Russian operation targeting Hillary Clinton's campaign making clear Russian hackers began targeting the campaign's emails within hours of a public appeal from Trump for them to do exactly that.

When the special counsel's office first indicted 12 GRU officers for hacking and leaking Democratic emails in July 2018, it mentioned that they only began targeting Hillary Clinton's campaign emails on July 27, 2016.

At the time, analysts noted that was the same day that then-candidate Trump said at a press conference , "Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing. I think you will probably be rewarded mightily by our press."

The special counsel's report doesn't explicitly mention that the GRU's decision was prompted by Trump's comments. Former Trump press secretary Sean Spicer claimed Trump had been joking when he made the appeal.

It does, however, make explicit the timing between Trump's statement and Russia's actions. "Within approximately five hours of Trump's statement, GRU officers targeted for the first time Clinton's personal office," the report says. "The investigation did not find evidence of earlier GRU attempts to compromise accounts hosted on this domain."