Nearly all Western nations have, over the past couple decades, added anti-counterfeiting measures to their currency. One popular mechanism currently in use in many nations is a small strip with holograms on it; reproducing holograms has historically been much more complex and expensive for criminals versus printing bogus copies of equivalent currency that did not sport holograms. Now, however, criminals have found a simple way to circumvent holograms.
What is the scam? How do crooks defeat holograms?
To learn more, please see my article in Inc. entitled How Criminals Are Defeating A Popular Paper Money Anti-Counterfeiting Measure.