Transcript for Russia's Digital Fingerprints on Election Hacking Code
can do this to you. Meanwhile, reports their laughing this off at the Kremlin saying, show us the proof. Here's Brian Ross with the evidence so far. Reporter: In Moscow tonight, a challenge to put up or shut up, with deputies for Russian president Vladimir Putin, and Russian reporters from a kremlin-funded TV network demanding the U.S. Produce any evidence it has implicating Russia in the hacking attack. Evidence that president-elect Donald Trump continues to maintain is far from certain. They're fighting among themselves, they're not sure. Reporter: But in fact, America's intelligence agencies are sure. Based largely on the forensic evidence the FBI and cyber security experts discovered inside the computers of the democratic national committee. They get in by what's called a spearfish attack. Reporter: Among the experts on the case, cyber security analyst Justin Harvey, who says the Russians first planted what's called a dropper or a beacon to send material back to Moscow. A dropper is a little tiny bit of software that calls back home and says, "I'm here, I was successful." Reporter: And it had a telltale Russian signature. With experts saying it was written in Moscow's time zone, and seemed to have gaps on what were Russian holidays, all entered by a distinctive keyboard. We saw the cyrillic alphabet being used. Reporter: And then U.S. Intelligence says the beacon transmitted to an internet address overseas. And it was an I.P. Address that had been previously seen in other russian-attributed attacks. Reporter: But it wasn't just forensics. The FBI has joined the CIA in the assessment that the Russian president was directly involved in the attack. Based on new information say comes directly from the Kremlin. And Brian, they say it was largely to help Donald Trump. Does this put increasing pressure from the president-elect to at least acknowledge this? Yes, with key Republicans raising questions about Rex tillerson, nominated for secretary of state. Brian, thank you. We turn next to the dangerous cold and the major snow storm from coast to coast. Tonight, the images of the firefighters, and the six-alarm fire.
This transcript has been automatically generated and may not be 100% accurate.