Q&A;: Pakistan's nuclear secrets

Who has them?
It had long been assumed that they were solely in the possession of Pakistan. However, investigations by the UN's nuclear watchdog, the International Atomic Energy Authority, into the Iranian nuclear programme - and later into Libya's - revealed that some of Pakistan's technologies had spread. It is also alleged that North Korea's nuclear bombs were built using Pakistani knowhow.

How did they get there?
Pakistan launched an investigation in November, and discovered that the founder of its nuclear programme, Abdul Qadeer Khan, was at the centre of the black market deals. He admitted, in a televised apology, that he accepted "full responsibility for all the proliferation activities conducted".

Was it just him?
There are six other suspects, but many are incredulous at the thought that Dr Khan could have acted without the wider support or knowledge of Pakistan's government and military elite. Mohamed ElBaradei, the head of the IAEA, has also said that the scientist is just "the tip of an iceberg" of the many people in many countries who form an international trafficking network. "There's a lot of chains of activity that we need to follow through on," he said.

Police in Malayasia are currently investigating whether a company controlled by the prime minister's son supplied nuclear components to Libya in a deal linked to Dr Khan. The Associated Press has reported that Pakistani officials told it Dr Khan occasionally ordered "disused equipment" to be sent to Malaysia for reconditioning before it was shipped to Iran, Libya and North Korea.

Who is Dr Khan?
The 69-year-old returned to Pakistan in 1976 after studying in Europe, and led the country's nuclear programme. The first tests of the country's nuclear deterrent against India in 1998 turned him into a national hero.

What will happen to him?
Pakistan's president, Pervez Musharraf, granted Dr Khan a pardon after his televised apology for his role in the trade. Putting such a popular figure on trial would have caused domestic difficulties for the president - opposition groups demonstrated on the streets in support of Dr Khan - and could also have led to embarrassing revelations about senior government and military officials.

Why did he do it?
"What is the motive of people? Money, obviously. That's the reality," Mr Musharraf said after granting the pardon. However, if there was a wider complicity on the part of elements of Pakistan's military and government, it is possible that money was not the sole motivation.

The US and Britain went to war against Iraq to stop proliferation. Why did they ignore Pakistan?
In part, there was an intelligence failure. Iraq's WMD programmes were believed to be more advanced than they actually were, while Iran's and Libya's, and the smuggling networks that created them, caught the international community off-guard. Little is known of the true extent of North Korea's programme, although it is believed that the country has enough reprocessed plutonium to manufacture a small number of bombs.

But there is also a question of politics. Pakistan, which borders Afghanistan, is an important US ally, and Washington is unwilling to put the kind of pressure on Mr Musharraf that would threaten his rule or make his job more difficult. The US state department has said that Pakistan has given it assurances that it will not allow its "technology to be used to help other nations that might be trying to develop weapons of mass destruction".