Suitcases of forged banknotes aren't just the stuff of heist movies and spy novels. Banks and governments around the globe are constantly working to prevent fraudsters from introducing fake cash into circulation – and some countries are more successful in their efforts than others.

Nations typically use parts per million (ppm), a metric borrowed from chemistry, to monitor counterfeit currency. They give a score by measuring the number of fake banknotes found in circulation for every one million genuine notes. Most nations aim to stay below the 15 ppm mark, though quite a few have seen an uptick in counterfeited cash.

Read on to discover how much fraudulent money is floating around in some of the world's major currencies, ranked from the lowest ppm rate to the highest. 

All dollar amounts in US dollars unless otherwise stated.