While the use of cash is declining around the world, it's still the most tangible, untraceable way to make payments. Every year, countries around the world print money, and many fraudsters do the same. Counterfeit bills are overall decreasing globally, but they still exist and pose a problem.
A way to monitor counterfeit currency is to use a metric called parts per million (ppm), which indicates one fake note per one million of real notes. In this gallery, we look at the most counterfeit currencies, according to ppm. Click on to find out what they are.