Well, put it this way:
Russia has denied having anything to do with it
But:
They lied about invading Ukraine, lied about MH17, lied about bombing civilian convoys in Syria, lied about the most spectacular state-sponsored drugs cheating in the history of sport (move over East Germany)
You cannot trust a word they say.
Then we have Trump, who is a foul mouthed mysogynist who's suddenly found himself in the White House.
Then we have the CIA, who you may mock, but compared with the above are bastions of reliability.
By the way, their allegations also include hints that Russian hackers did indeed attempt to gain access to the voting machines (which if the Wisconsin experience is anything to by seem to be impressively accurate) but no evidence that they succeeded in doing any damage.
At the very least, the President elect should be saying that he will launch a cross-party Senate investigation into this when he becomes president. He seems to be dimissing his own intelligence services and believing the word of the criminals above. And "I don;t need intelligence briefing?" What The Funicular?
He needs an intelligence transplant :-)