(CNN) -- The story of how I became a national figure in the media is widely known, but few people know what I actually did for the CIA.





I was a covert operations officer specializing in nuclear counter proliferation -- essentially, making sure the bad guys didn't get the bomb.





My job was to create and run operations that sought to peer into the procurement networks and acquisition chains of rogue nations. It was intense, tactical, creative and demanding. I believed that there was no more important work to be done.





I resigned from the CIA in 2006 because it was no longer possible to do the covert work for which I was highly trained and which I loved. This happened because in 2003, my covert identity was revealed in retaliation against my husband, Ambassador Joe Wilson, who wrote an op-ed piece in which he accused the White House of distorting the intelligence that was used to draw us into the Iraq war.





But I did not lose my belief that the danger of nuclear terrorism was the most urgent threat we face. Nor did I lose my passion for working, albeit in a new way, to address that threat. I am working on this issue now as part of the international Global Zero movement, in which political, military and faith leaders, experts and activists strive for the worldwide elimination of all nuclear weapons.





We know that terrorist groups have been trying to buy, build or steal a bomb.





In the past two decades, there have been at least 25 instances of nuclear explosive materials being lost or stolen. There is enough highly enriched uranium, or HEU, in the world today to build more than 100,000 bombs.





Terrorists looking to buy or steal HEU could look to the approximately 40 countries with nuclear weapons materials. And then there are rogue individuals out there who are running black markets selling nuclear materials and technology.





Pakistan's Dr. A. Q. Khan did it for years before my group at the CIA brought him down in December 2003 after catching him red-handed selling a full-scale nuclear bomb to Moammar Gadhafi's regime in Libya.





If terrorists manage to get their hands on enough HEU, they could smuggle it into a target city, build a bomb and explode it. A hundred pounds of highly enriched uranium could fit in a shoebox, and 100,000 shipping containers come into the United States every day.





The nuclear threat is not limited to terrorism.





There are also the dangers of proliferation and accidental or unauthorized nuclear launch. Today, nine countries have more than 23,000 nuclear weapons, and the U.S. and Russia still maintain thousands of nuclear weapons on hair-trigger alert, poised for launch within a few minutes.





The only way to eliminate the danger that nuclear weapons will be used by countries in conflict, by accident or by terrorists is to lock down all nuclear materials and eliminate all nuclear weapons in all countries: global zero.





Today we have a real opportunity to set the course to global zero. U.S. President Obama and Russian President Dmitry Medvedev, whose countries have 22,000 nuclear weapons or 96 percent of the world's stockpile, are signing an agreement to reduce their strategic nuclear arsenals by a third each. This is the most significant arms reduction treaty in two decades and a crucial first step.





Next week, Obama is hosting the leaders of 48 countries at a summit in Washington to address the global nuclear threat and initiate programs to secure all nuclear materials worldwide. With the U.S. and Russia leading the way, 2010 could mark the beginning of the end of nuclear weapons.





But achieving global zero will take years, a realistic plan of action and tremendous amounts of political will. In February, leaders of the Global Zero movement met in Paris, France, and outlined a step-by-step plan to eliminate all remaining nuclear weapons.





The plan, backed by hundreds of former heads-of-state, foreign ministers, national security advisers and military commanders, calls in its first phase for the U.S. and Russia to cut their arsenals to 1,000 total warheads each. All other countries with nuclear weapons would freeze their arsenals,
Who is Valerie Plame Wilson? What does Valerie Plame Wilson think is the #1 threat right now? What is the No.1 Threat faced right now?
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question: Who is Valerie Plame Wilson?, answer: covert operations officer specializing in nuclear counter proliferation | question: What does Valerie Plame Wilson think is the #1 threat right now?, answer: danger of nuclear terrorism | question: What is the No.1 Threat faced right now?, answer: nuclear terrorism