North Korea has been printing fake US$100 bills for 25 years

According to the Los Angeles Times:

The counterfeiting operation began a quarter of a century ago, he recalled, at a government mint built into a mountain in the North Korean capital.

Using equipment from Japan, paper from Hong Kong and ink from France, a team of experts was ordered to make fake U.S. $100 bills, said a former North Korean chemist who said his job was to draw the design.

...

By 1989, millions of dollars' worth of high-quality fakes were showing up around the world. U.S. investigators dubbed them "supernotes" because they were virtually indistinguishable from American currency. The flow of forged bills has continued ever since, U.S. officials say, despite a redesign intended to make the cash harder to replicate.

U.S. officials called the operation an economic act of war.