The admission by the father of the Pakistan nuclear bomb, Dr Abdul Qadeer Khan, that he gave nuclear secrets to other countries has stunned world nuclear experts.
Khan was sacked as a government special adviser on 31 January
It will also strengthen the determination of the United States to try to stop nuclear proliferation.
The countries Dr Kahn is said to have helped are North Korea, Libya and Iran.
Dr Gary Samore of the International Institute for Strategic Studies in London, an expert on North Korea in particular, said: "This is by far the worst example of nuclear proliferation in world history.
"It is clear that AQ Kahn and his confederates from the laboratory which he ran have been doing this for 15 years.
"They did it partly for money, but AQ Khan also believed that the spread of nuclear weapons, especially to some Islamic countries, was a good thing and lessened the threat of hegemony by the United States."
The story goes back to the mid-1970s and shows how one determined operation can avoid the international measures to prevent the spread of nuclear weapons.
Dr Khan is believed to have got the design of a centrifuge for enriching uranium to weapons grade from an Anglo-Dutch-German company called Urenco, where he was working.
He used this as the basis for building Pakistan's own bomb.
The Urenco blueprint or developments of it are what he is said to have given to North Korea, Iran and Libya.
But he also handed over, at least to Libya, designs for a nuclear warhead.
Khan is widely seen as a hero for giving Pakistan a nuclear deterrent
Libya is said by the New York Times to have paid $50m for a design which resembled a Chinese warhead once given to Pakistan.
It was the admission by Iran last year that it had obtained centrifuge designs on the black market that started the investigation along the trail which led back to Pakistan.
Iran has since signed an Additional Protocol with the UN's nuclear agency, the International Atomic Energy Agency (IAEA), under which inspections will be much more intense.
Libya has also agreed to open up its own nuclear programme to inspection by American and British experts and the IAEA.
Dr Khan used front companies around the world to make purchases, sent them to the Gulf state of Dubai and from there they were delivered to their eventual destinations.
The question now is whether the Pakistan Government or senior people within it knew what was going on.
"We may never know, " said Dr Samore," but many will think it unlikely that they could have done so much for so long on their own."
The suspicion is that North Korea might have provided Pakistan with missile technology in return for nuclear expertise.
That would have required government to government contacts.
If this had happened in a country other than Pakistan, the drums would be beating loudly in Washington.
Pakistan might have qualified for membership of the axis of evil.
But because Pakistan's President General Musharraf is such a close ally of the United States in the war on terror, a scenario seems to have been agreed under which Dr Khan would make his public admission but would absolve the Pakistani Government.
It is a procedure which the Americans may, for diplomatic reasons, accept.
Certainly it will make Washington, supported by its allies, even more determined to investigate and try to stop the spread of nuclear technology and weapons.
But the revelation has shown how the black market can operate under the nose of the IAEA.
Mohamed ElBaradei, the Director General of the IAEA, said on Thursday that the Pakistan connection was the "tip of an iceberg".
He had previously warned a World Economic Forum in Davos of "a very sophisticated and complex underground network of black market operators ... not that much different from organised crime cartels".
IAEA spokesperson Melissa Fleming said that the IAEA was aware of a network that involved "players in five countries".
Dubai and Malaysia are believed to be among these five, according to informed sources.
"This needs to be thoroughly investigated and stopped in its tracks," she said.
"An urgent priority for the IAEA is to find out if others have bought into the nuclear network."
The IAEA board meets on 8 March to review its monitoring programmes in Iran and Libya.
North Korea has withdrawn from the nuclear Non-Proliferation Treaty.