NEW YORK: Donald Trump on Thursday tapped former New York mayor Rudy Giuliani to advise his incoming administration on cyber security following outcry over Russian hackers´ apparent attempt to meddle in the election.

Giuliani, 72, dubbed America´s mayor for his leadership in the wake of the 9/11 attacks, said last month he had taken himself out of the running for a cabinet job after coming under scrutiny in the US media over business dealings that could post conflicts of interest.

Thursday´s announcement from the president-elect called cyber intrusion "the fastest growing crime in the United States and much of the world" and said it was a "major threat" to national security.

The New York billionaire and incoming Republican president said "immediate attention" and "input from private sector leaders" was required to "help the government plan to make us more secure."

Trump said he had asked Giuliani to initiate this process "because of his long and very successful government career in law enforcement" and his experience providing security solutions in the private sector.

Trump on Wednesday admitted for the first time that Russia was behind the hacking of Democratic Party computers during the election campaign.

He has promised that as soon as he takes office on January 20 he will give a team 90 days to come up with a plan to halt cyber attacks.

But the announcement stopped short of giving Giuliani a formal title, leaving unclear the remit of the former US attorney, who forged a tough reputation in the 1980s for indicting members of the New York mafia.

The president-elect said Giuliani would be "sharing his expertise and insight as a trusted friend concerning private sector cyber security problems and emerging solutions developing in the private sector."

The statement said Trump intends to meet company executives to obtain "experiential and anecdotal information" about ways to counter intrusions such as hacking and data theft.

Giuliani, a Trump surrogate during the campaign, runs an international security consulting firm and had been a candidate for secretary of state until he said last month that he had withdrawn his name.

At that time Trump said Giuliani remained a close personal friend, adding that "as appropriate, I will call upon him for advice and can see an important place for him in the administration at a later date."