President-elect Donald Trump says he is knowledgeable in the field of cyber-hacking and "no computer is safe" when it comes to keeping information private.

Trump's statement to reporters during his annual New Year's Eve bash expressed new scepticism about the security of online methods of communication his administration is set to use.

"You know, if you have something really important, write it out and have it delivered by courier, the old-fashioned way ... because I'll tell you what: no computer is safe," Trump said.

The billionaire businessman has repeatedly cast aside allegations by US intelligence agencies that Russia tried to influence the presidential election through hacking.

President Barack Obama ordered sanctions on Russian spy agencies last week, closed two Russian compounds, and expelled 35 diplomats the US alleged were really spies. The Russian government has denied the allegations.

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Trump plans to meet intelligence officials in the coming days to learn more about the allegations. He said he wants US officials "to be sure, because it's a pretty serious charge". He pointed to intelligence failures over the existence of weapons of mass destruction in Iraq before the US invasion.

And the 70-year-old president-elect declared himself well-versed in the field of hacking.

"I know a lot about hacking," he said, "and hacking is a very hard thing to prove, so it could be somebody else."

He added cryptically that he also knows "things that other people don't know. And so, they cannot be sure of the situation".

While Trump may be against computers, he's still planning lots of Twitter use.

When an ABC News interviewer asked whether Trump would continue his highly unusual - and deeply controversial - approach of making major policy statements over Twitter, his communications director Sean Spicer replied, "Sure, why not?"

With all due respect," he continued, "I think it freaks the mainstream media out that he has this following of over 45-plus million people that follow him on social media, that he can have a direct conversation."

Spicer added: "Business, as usual, is over ... There's a new sheriff in town."