Supernote

A superdollar (also known as a superbill or supernote) is a very high quality counterfeit United States one hundred-dollar bill, alleged by the U.S. Government to have been made by unknown organizations or governments. In 2011 government sources stated that these "counterfeit bills were in worldwide circulation from the late 1980s until at least July 2000" in an extradition court case.

It is important to note that while there are many features on "super notes" that can be detected with today's technology, new, more sophisticated super notes are always being produced. No current technology can guarantee catching 100% of the super notes in circulation.

Various groups have been suspected of creating such notes, and international opinion on the origin of the notes varies. The U.S. Government believes it most likely that the majority of these notes were produced in North Korea. Over $35 million of $100 bills were produced by British criminals arrested in 2002. The name derives from the fact that the quality of the notes exceeds that of the originals.

More $100 bills circulate in Asia, where U.S. currency is often seen as a safer investment than local currency, and many seizures of supernotes are associated with persons from Korea, Russia, and the Middle East.

A new $100 bill design intended to thwart counterfeiting, incorporating a "3D security ribbon", colorshifting numerals and drawings, and microprinting, entered circulation in 2013.

Supernotes are said to be made with the highest quality of ink printed on a cotton/linen blend, and are designed to recreate the various security features of United States currency, such as the red and blue security fibers, the security thread, and the watermark. Moreover, they are printed using an intaglio printing process or with engraved plates, the same process used by the U. S. Government for legitimate notes. In most counterfeiting, offset printing or color inkjet and laser printing are most common means of making counterfeit money.

...
Wikipedia