Washington DC Metro Farecard Hack
Thieves took a legitimate paper Farecard with $40 in value, sliced the card’s magnetic strip into four lengthwise pieces, and then reattached one piece each to four separate defunct paper Farecards. The thieves then took the doctored Farecards to a Farecard machine and added fare, typically a nickel. By doing so, the doctored Farecard would go into the machine and a legitimate Farecard with the new value, $40.05, would come out.
My guess is that the thieves were caught not through some fancy technology, but because they had to monetize their attack. They sold Farecards on the street at half face value.