Russian hackers targeted 21 U.S. state election systems in the 2016 presidential race and a small number were breached but there was no evidence any votes were manipulated, a Homeland Security Department official told Congress on Wednesday, Reuters reported.
Jeanette Manfra, the department's acting deputy undersecretary of cyber security, testified before the Senate Intelligence Committee.
U.S. intelligence agencies have concluded the Kremlin orchestrated a wide-ranging influence operation that included email hacking and online propaganda to discredit Democratic presidential candidate Hillary Clinton and help Donald Trump, a Republican, win the White House in November.
The Russia issue has cast a shadow over Trump's first five months in office. The extent of interference by Russian hackers, and whether they or others could interfere in future elections, has been the source of speculation and media reports for months.
Russia has repeatedly denied responsibility for any cyber attacks during the election. Trump has variously said Russia may or may not have been responsible for hacking but has dismissed allegations his associates colluded with Moscow as "fake news."
Manfra and other officials testifying on Wednesday said U.S. elections are resilient to hacking in part because they are decentralized and largely operated on the state and local level.
Senator Angus King, an independent from Maine who caucuses with the Democrats, voiced skepticism, saying only a small number of votes in key battleground states would need to be altered to tip the scales in an election.
"A sophisticated actor could hack an election simply by focusing on certain counties," King said. "I don't think it works just to say it’s a big system and diversity will protect us."
Mark Warner, the top Democrat on the Senate panel, expressed frustration at Manfra's refusal to identify which states had been targeted. Arizona and Illinois last year confirmed that hackers had targeted their voter registration systems.
Samuel Liles, another senior DHS cyber official, likened states targeted or scanned to a thief walking by homes to scout for weaknesses, and breaches to breaking through a front door.