He's baaaack.The Typhoid Mary of nuclear proliferation is a free man again, and that has a lot of people worried. A. Q. Khan, father of the Islamic Bomb and the man who also helped sire North Korea's nuclear device, Iran's bomb-in-the-making and Syria's interrupted attempt, was freed from home confinement this week by a Pakistani court. Khan is a national hero in Pakistan as the man who took that country into the nuclear age to challenge neighboring India's atomic arsenal and permanently raise tensions in the region. Along the way he sold nuclear technology, designs and equipment to some of Israel's bitterest enemies. Khan's customers include rogue regimes we know about and other countries and terror groups we don't know. Since his 2003 arrest, members of his network have popped up in Saudi Arabia, Malaysia, Libya, Iran, Dubai and other places that do not wish the Jewish state well. The Times of India, in what may be more wishful thinking than informed reporting, suggests the Mossad may be gunning for Khan. "Can Pakistan's nuclear scientist A. Q. Khan be on a secret hit list of the frighteningly efficient Mossad of Israel? He could, particularly since six of his closest associates, all nuclear scientists from the Khan Research Laboratories, apparently are," the Times reported this weekend. It cites a new edition of author Gordon Thomas's book about Mossad, Gideon's Spies, saying 9/11 conspirator Khalid Sheikh Mohammed told US investigators Khan had met with Osama bin Laden and other top al-Qaida figures in April 2003, raising fears in the US and Israel of a "dirty bomb" plot. KHAN'S RELEASE is a stark reminder that for all the fretting over Iran's nuclear ambitions, Pakistan poses a very real threat right now. Unlike Iran, it already has the bomb - actually about 100 of them - which Washington spends millions to secure while being refused information about where they are. One of the dangers posed by Khan's efforts is that once Iran builds its own nuclear device it will not only have a weapon with which to blackmail its rivals and enemies, but it will probably spark a regional nuclear arms race. Pakistan remains a weak, corrupt state that cannot control its own territory and is a prime candidate for takeover by Islamic extremists. Khan's release was widely celebrated there, but condemned abroad, particularly in the United States which, along with the UN and other countries, has been denied access to Khan and his network to ask about his customers and what they bought. In addition, we've been pumping billions into the Pakistani military since 9/11 to help in the fight against the Taliban and al-Qaida, but we don't even know whose side they're on. Even the former president, Pervez Musharraf, was uncertain about the loyalty of many in his army and intelligence services. Author Thomas Ricks said on Meet the Press this week that the Pakistani military is, in many ways, the problem: "You have a lot of al-Qaida and Taliban supporters wearing Pakistani military uniforms." Pakistan - not Iraq, Afghanistan, Iran or the Arab-Israeli conflict - is the top foreign policy challenge facing the Obama administration, according to a forthcoming Pentagon review. THE STATE DEPARTMENT said Khan remains "a serious proliferation risk," and the damage he and his network have done will last "for years to come." Ambassador Richard Holbrooke, in the region this week on his first visit as the special representative for Pakistan and Afghanistan, is expected to ask Pakistani officials for assurances that Khan won't be allowed to resume his old trade, but it would be a mistake to accept Islamabad's promise to take "all necessary measures to promote the goals of nonproliferation." A doubtful Rep. Howard Berman, chairman of the House Foreign Affairs Committee, called Khan "the worst proliferator of nuclear weapons technology in history," and said more than five years after his arrest it remains "unclear whether the illicit smuggling network he created was fully dismantled." He hinted that continued refusal to permit US access to Khan could impact Congressional consideration of aid to the Islamabad government. Khan's own web page (www.draqkhan.com.pk) boasts that he is "endowed (by God) with exceptional intellectual capabilities and creative abilities" and "destined to make history in the elevation of nations." The explosion of six nuclear devices in May 1998 was "entirely due to his efforts," as was the successful test-firing of intermediate-range ballistic missiles in 1998 and 1999, according to his web page. Failure in Pakistan - with its nukes and missiles, history of proliferation, ties to al-Qaida and the Taliban, unstable and corrupt government, periodic coups, and the growing influence of Islamic extremist factions even inside its own military and intelligence services - could result in a nuclear-armed mujahidin state. A state that worships a man who sells nuclear secrets to some of the world's most notorious rogue regimes may be a bigger threat than the crazy, Israel-hating leader of Iran.