A Department of Homeland Security official informed the Senate Intelligence Committee on June 21 Russian hackers targeted 21 states during the 2016 election.
"As of right now, we have evidence that election-related systems in 21 states were targeted," said Jeanette Manfra, the department's acting deputy undersecretary of cyber security, while testifying for the Senate Intelligence Committee, Reuters reports.
Of those 21 states, Manfra revealed a few were even breached, supporting the earlier testimony of Samuel Liles, acting director of the DHS cyber division.
"A small number of networks were exploited -- they made it through the door," Manfra said, BBC reports.
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Bill Priestap, assistant director of the FBI’s counter-intelligence division, said the hackers also copied data from some states "to understand what it consisted of" to use for attacks in the future, reports the Los Angeles Times.
Manfra emphasized there was no evidence to prove any of the 21 state votes were tampered with.
She proceeded to assure the committee that elections are hard to hack. Along with other officials, she explained this is because elections are decentralized and occur on the state and local levels.
Many debate the validity of that assertion, noting that only a tiny number of votes in an area could alter an election's outcome.
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"A sophisticated actor could hack an election simply by focusing on certain counties," said Independent Sen. Angus King of Maine, who caucuses with the Democrats. "I don't think it works just to say it’s a big system and diversity will protect us."
Meanwhile, due to confidentiality agreements, Manfra had refused to disclose which states had been targeted -- a move some disagree with.
Democratic Sen. Mark Warner of Virginia, the vice chairman of the Senate Select Committee on Intelligence, expressed frustration over the information that was withheld.
"I just fundamentally disagree [with it]," he said, adding the country was "not any safer" in keeping the states' identity a secret.
The day before, Warner released a public letter urging the DHS to divulge more information.
"I strongly believe that the answer to such efforts to interfere in our elections is to harden our cyber defenses and to thoroughly educate the American public about the danger posed by these attacks," he wrote. "I therefore urge you to work closely with state and local election officials to disclose publicly which states were targeted, to ensure that they are fully aware of the threat, and to make certain that their cyber defenses are able to neutralize this danger."
Republican Sen. Marco Rubio of Florida was also worried.
"It is important Americans understand how our voting systems work and communicate that in real time," he said.
The public already knows at least two states the Russians had their eyes on. Arizona and Illinois confirmed in 2016 hackers had targeted their voter registration systems.