North Korea has developed a nuclear weapons program despite poverty and international sanctions, using home-grown technology and virtually free labor to cut costs, experts said.<br />South Korean government analysis has put North Korea's nuclear spending at $1.1 billion to $3.2 billion overall, although experts say it is impossible to make an accurate calculation given the secrecy surrounding the program, and estimates vary widely.<br />However, the weapons that North Korea has tested thus far are comparatively small and based mostly on less sophisticated fission, or atomic bomb, technology.<br />The isolated North's claim that its fourth and most recent test, conducted last week, was of a more advanced and powerful hydrogen bomb has been widely doubted, although experts said it is possible Pyongyang took the intermediate step of boosting an atomic bomb with hydrogen isotopes.
