The FBI has arrested 13 people on charges that they participated in a gang that stole more than $1 million via cash-advance kiosks at 11 casinos and resorts, according to an article in InformationWeek.

The related indictment, unsealed Friday, says the gang “stole the money by exploiting a gap—which required multiple withdrawals all within 60 seconds—in Citibank’s electronic transaction security protocols.” The gang primarily targeted casinos and resorts in Las Vegas and Southern California, the article says.