The hush-hush meeting, which was first revealed last week by Subang parliamentarian R Sivarasa during his debate with Perkasa information chief Ruslan Kassim, was held at the luxury Plaza Hotel in Manhattan.
Malaysiakini has confirmed the Najib-Soros meeting with a source who has direct knowledge of the event.
The prime minister's meeting with Soros, who is accused of funding Malaysian NGOs to push for regime change, took place on Sept 27, 2010.
It is believed that at least one other top Umno leader was present at the get-together.
Najib, who became prime minister in 2009, made his maiden speech at the UN General Assembly in New York on the same day he met with the billionaire financier.
In his UN speech, Najib mooted a 'global movement of the moderates' to reclaim the agenda for peace and pragmatism.
On the sidelines of the general assembly, Najib also met with UN secretary-general Ban Ki-moon and held talks with several heads of government.
Among those who accompanied Najib on that trip were his wife Rosmah Mansor, Foreign Minister Anifah Aman and Malaysian ambassador to the United States Jamaluddin Jarjis.
Umno's whipping boy
The man whom Najib met has been one of Umno's favourite whipping boys.
Soros, a controversial currency trader and philanthropist, was blamed for bringing financial ruin to Malaysia during the 1997-98 economic meltdown, and more recently, for seeking to oust BN by allegedly funding anti-government NGOs.
Over the past few weeks, a gaggle of pro-government bloggers and Umno-owned Utusan Malaysia have blasted NGOs, including human rights group Suaram and polls reform movement Bersih, for receiving funding from Soros' Open Society Foundations.
Malaysiakini, too, came into the line of fire over its links with MDLF, an investment fund that owns a 29 percent stake in the independent news website. MDLF raises capital from banks, governments and funding agencies, which included Soros' foundation.
On Sunday, former prime minister Dr Mahathir Mohamad joined the chorus by accusing Malaysiakini of working with Soros to engineer a regime change so as to "put his nominees as prime minister and ministers in the Malaysian government".
"My view of Soros is that he is still a rogue currency trader and he compounds this evil by using the money to put his kind of people to rule the countries targeted by him. And Malaysia obviously is one of his targets," Mahathir wrote in New Straits Times.
Connecting two disparate dots, he came to a wild conclusion: "A vote for the opposition is a vote for Soros."
Rogue central bank
Ironically, when Mahathir was prime minister, Malaysia's Bank Negara was known as a rogue central bank for dabbling in high-risk currency speculation - it lost a whopping RM5.7 billion to the likes of Soros in the early 1990s.
Last month, Malaysiakini revealed that Mahathir, despite his animosity with Soros, had written to the billionaire for his support to lend his name to the former premier's Global Peace Forum project to outlaw war as a means to solve human conflicts.
According to international weekly Economist, politics in Malaysia has increasingly turned toxic in the run-up to the crucial 13th general election, with Umno and Umno-friendly media attacking any organisation deemed sympathetic to the opposition.
"All the old canards about these sorts of groups being in the pay of Zionists, America or George Soros, a foreign financier, have been trotted out," it said in an article that was published earlier this week.
"It is not clear whether such slanders still impress Malaysia's voters, especially its Muslims. They are certainly a sign of desperation."