Russians penetrated US voter systems, DHS cybersecurity chief tells NBC

• Russians targeted 21 states' voter registration rolls during the 2016 presidential election.
• Of those, a "small number" were successfully penetrated, according to a Homeland Security Department official tasked with protecting elections from hacking threats.
• U.S. officials have said there is no evidence that any states' voter registration rolls were tampered with.

Russians penetrated multiple states' voter registration rolls in the 2016 presidential election, the head of cybersecurity at the Department of Homeland Security told NBC News on Wednesday.

Of the 21 states targeted by Russians in the election, several were successfully penetrated, said Jeanette Manfra, in an exclusive interview with NBC.

U.S. officials have said there is no evidence that any states' voter registration rolls were tampered with or at all altered by the foreign intrusions.

Manfra, whose role is to protect American elections from hacking, did not specify which states had been successfully penetrated, saying she could not publicly disclose classified information.

"We saw a targeting of 21 states and an exceptionally small number of them were actually successfully penetrated," Manfra told NBC.

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Acting Director of Homeland Security's Office of Intelligence and Analysis Cyber Division Sam Liles (L) and Homeland Security Undersecretary Jeanette Manfra (R) testify during a hearing before the Senate (Select) Intelligence Committee June 21, 2017 on Capitol Hill in Washington, DC.

The Washington Post previously reported that computer systems in Illinois and Arizona were both successfully penetrated.

Manfra's interview arrived alongside other U.S. officials' recent warnings that Russian hackers may attempt to influence the 2018 midterm elections. In an interview on Tuesday, Secretary of State Rex Tillerson said Russia is already trying to interfere in the upcoming congressional elections.

"If it's their intention to interfere, they are going to find ways to do that," Tillerson said in a Fox News interview.

In late January, CIA Director Mike Pompeo said he has "every expectation" that Russia will try to target the midterms.

"I have every expectation that they will continue to try and do that," Pompeo said in an interview with the BBC, "but I'm confident that America will be able to have a free and fair election [and] that we will push back in a way that is sufficiently robust that the impact they have on our election won't be great."

In September, the Homeland Security Department informed election officials in the 21 targeted states that Russian government hackers had tried to penetrate their voting machines in 2016.