Many Democrats — including presidential nominee Hillary Clinton — have blamed Moscow for trying to tilt the election in favor of GOP rival Donald Trump with the digital attacks. | AP Photo | Getty Computer researcher to Congress: 'It's possible' for hackers to alter election

Hackers could influence the outcomes of November’s elections, a computer science professor who has demonstrated security weaknesses in voting machines told lawmakers on Wednesday.

“It’s possible,” said Andrew Appel, a professor at Princeton University, at a House Oversight IT subcommittee hearing focused on election cybersecurity.


But Appel, who has hacked voting machines used in many states, was the only one to reply affirmatively when subpanel Chairman Will Hurd (R-Texas) asked for a "yes" or "no" answer to the question, "Can a cyberattack change the outcome of our national elections?”

The four other people testifying — including a secretary of state, the chairman of the federal agency that assists with elections, a top Department of Homeland Security cyber official and the head of a public policy firm's division focused on voting rights — all essentially answered “no.”

The DHS official, Assistant Secretary for Cybersecurity and Communications Andy Ozment, later clarified his answer to stress that DHS was not resting on its laurels.

“We have to always be vigilant,” he said. “In the field of cybersecurity, we can never relax.”

But Rep. Ted Lieu (D-Calif.) wasn't completely soothed by the responses from the four witnesses.

"My view is they don’t have to hack 50 states," he said. "In a close presidential election, they just need to hack one swing state. Or maybe one or two. Or maybe just a few counties in one swing state."

Wednesday's hearing comes as the Obama administration is investigating whether Russia is behind a series of election hacks targeting Democratic Party organizations, current and former government officials and multiple state voter registration databases.

Many Democrats — including presidential nominee Hillary Clinton's campaign — have blamed Moscow for trying to tilt the election in favor of GOP rival Donald Trump with the digital attacks.

But Trump pushed back at the theory during Monday's first presidential debate.

"It could be Russia, but it could also be China, but it could also be lots of other people, it also could be someone sitting on their bed that weighs 400 pounds, OK?" he said.

On Capitol Hill Wednesday, FBI Director James Comey gave perhaps the Obama administration's most direct hint yet that the Kremlin was orchestrating the cyber campaign.

“We are doing an awful lot of work through our counterintelligence investigators to understand just what mischief is Russia up to in connection with our election," Comey told the House Judiciary Committee during the annual FBI oversight hearing.

Reportedly, U.S. intelligence officials have " high confidence" that Moscow is behind at least the hack at the Democratic National Committee, which kicked off this summer's string of digital intrusions.

Dumps of documents likely stolen during these digital break-ins fueled allegations of DNC bias against Sen. Bernie Sanders' presidential bid and forced the resignation of DNC Chairwoman Debbie Wasserman Schultz.

Since then, a steady stream of leaks have continued to frustrate Democratic officials, and embarrass other prominent figures, such as Colin Powell.

At the Washington Ideas Forum on Wednesday, CIA Director John Brennan acknowledged that Russia has an "active" history "globally" of trying to "influence political developments."

Intelligence officials are factoring in Moscow's penchant for meddling as they investigate the U.S. election hacks, Brennan explained.

"What we do at the CIA is to look at country's capabilities, look at their intent and look at what they have done in the past, and determine whether if something that certainly looks like a duck, smells like a duck and flies a duck, whether it is a duck or not," he said.

Brent Griffiths contributed to this report.