US intelligence officials say Russian President Vladimir Putin personally "ordered" a campaign to influence November's election in Donald Trump's favour.
The President-elect however says any efforts by the Russians had "absolutely no effect" on the outcome. It's the first time Mr Trump has acknowledged Russians were behind cyber attacks on US institutions last year.
In a 25-page report released on Friday (US time), officials say Russia aimed to "undermine the US-led liberal democratic order" and "denigrate" rival Hillary Clinton.
"There was absolutely no effect on the outcome of the election, including the fact that there was no tampering whatsoever with voting machines," Mr Trump said in response.
It hasn't even been a day since he suggested the hacking never even happened.
"The Democratic National Committee would not allow the FBI to study or see its computer info after it was supposedly hacked by Russia," he tweeted. "So how and why are they so sure about hacking if they never even requested an examination of the computer servers?"
The New York businessman, who is to be inaugurated as president on January 20, said he would appoint a team to give him a plan within 90 days of taking office on how to prevent cyber attacks - but suggested that he would keep their recommendations secret.
Mr Trump says he had a "constructive" meeting with members of the US intelligence agencies.
"Russia, China, other countries, outside groups and people are consistently trying to break through the cyber infrastructure of our governmental institutions, businesses and organisations including the Democrat National Committee," he said in a statement afterwards.
"The methods, tools and tactics we use to keep America safe should not be a public discussion that will benefit those who seek to do us harm."
Russia has denied any involvement in the cyber attacks.
The briefing coincided with deep tension between the intelligence agencies and Mr Trump, who has disparaged their conclusions that Russia's cyber attacks were intended to interfere in the election by hacking Democratic Party institutions and Clinton campaign staff.
In a telephone interview with the New York Times before the briefing, Trump had dismissed the controversy.
"China, relatively recently, hacked 20 million government names," he said in a telephone interview with the New York Times, referring to the Office of Personnel Management breach in 2014 and 2015.
"How come nobody even talks about that? This is a political witch hunt."
Trump's questioning of the intelligence agencies' conclusions have not only drawn the ire of Democrats but also fellow Republicans.
Senators John McCain and Lindsey Graham, both Republicans who took part in a Senate hearing with US spy chiefs on Thursday, have called for further congressional inquiries.
Reuters / Newshub.