According to high-level North Korean defectors, since the 1970s, revenue accumulated through foreign currency, revenue which is wholly separate from the official economic organs of the state, is of economic significance. The scale of its significance remains unknown and is a closely guarded secret, however. More recently, this foreign currency is said to have been also derived from the over 100,000 North Korean migrant workers sent around the world, and who contribute the lionshare of their income to this "Royal Court" fund. Other banking, trade, and financial ventures (many of which are illicit) are also said to be significant contributors. The fund is reported to be primarily tasked with providing the capital needed to develop the country's military technology (above all else, its nuclear weapons program), as well as contributing to a system of "gift giving" for the country's political, military and business elite.