This is the most obvious form. Under Title 18 of the U.S. Code, Section 471, whoever "with intent to defraud, falsely makes, forges, counterfeits, or alters any obligation or other security of the United States" is committing a federal crime. Counterfeit notes mimic legal tender but lack government authorization. Once a bill is identified as counterfeit, it ceases to be "tender" of any kind—it becomes evidence of a crime.
The most dangerous illegal tender isn't crude; it's nearly perfect. "Superdollars" are counterfeit $100 bills so precise that they fool ultraviolet scanners and pen testers. Intelligence agencies suspect North Korea produces these supernotes, using them to purchase goods and destabilize the U.S. economy. While the average citizen rarely sees one, their existence floods black markets with high-quality illegal tender. Illegal Tender
Money is often described as a social contract—a belief system where a piece of paper or a metal disc holds value simply because we agree it does. Governments back this belief with the "full faith and credit" of their treasury. But what happens when that trust is broken? What happens when the currency in your hand is not a tool of trade, but a weapon of deceit? This is the most obvious form