Counterfeiting of the currency of the United States is widely attempted. According to the United States Department of Treasury, an estimated $70 million in counterfeit bills are in circulation, or approximately 1 note in counterfeits for every 10,000 in genuine currency, with an upper bound of $200 million counterfeit, or 1 counterfeit per 4,000 genuine notes. However, these numbers are based on annual seizure rates on counterfeiting, and the actual stock of counterfeit money is uncertain because some counterfeit notes successfully circulate for a few transactions. History Article I, Section 8 of the U.S. Constitution gives Congress the power to "provide for the Punishment of counterfeiting the Securities and current Coin of the United States". This has been considered by federal courts to be an exception to freedom of speech. Counterfeiting was so prevalent in the early nineteenth century that contemporary accounts like those from author John Neal claimed that as much as half of the US currency in circulation was counterfeit. By the 1830s, American newspapers began listing instructions for identifying counterfeits. Because currency was issued by individual banks, there were approximately 5,400 types of counterfeit bills in the US by the 1860s. Shortly after the Civil War, it was estimated that one third to one half of the nation's currency was counterfeit. Counterfeit money thus posed a major threat to the economy and financial system. When the Secret Service was founded in 1865, its primary task was to minimize counterfeiting. In 2001, the U.S. Treasury estimated the prevalence of counterfeit U.S. currency in circulation at less than 0.01%. Operation Bernhard During World War II, Nazi Germany successfully produced high-quality counterfeits of American dollar and Bank of England pound notes, although few ever were circulated thoroughly. Superdollar Superdollars, very high quality counterfeit one hundred-dollar bills, were some of the most widely distributed counterfeit American dollar bills and were still being produced after 2007. The Congressional Research Service has conducted a study and concluded with an accusation that North Korea was responsible for their production, but Pyongyang denied any involvement with Superdollar. Peru 2001 CB-B2 series $100 bill incident In 2005, Peruvian Banks ceased to accept $100 bills from the 2001 series CB-B2, due to a detection in a series of counterfeit bills in Peruvian circulation. The differences between them and genuine bills were reportedly minuscule and difficult to detect. According to Peruvian news reports, a printing plate from the