English: Counterfeit 100 dollar bill, dated 1974 but probably made later. Forgery of a 1974 United States Department of the Treasury issue 100 dollar bill, overstamped with "Contrefaçon" on both sides. On display at the British Museum, London. Two-thirds of the US currency is estimated to be in circulation outside the USA. This makes controlling counterfeiting even more difficult. The 100 dollar bill is the most tempting for counterfeiters because of its high value. The US government has accused North Korea of producing counterfeit 100 dollar bills, known as "superdollars".