Federal prosecutors in New York say cyber-criminals stole $45 million by hacking their way into a database of prepaid debit cards.
One cybercrime expert says the heist was on the "high-end" of what can be done by cybercriminals who exploit banking systems connected to the Internet.
The global network of thieves drained cash machines within hours.
The thefts involved thousands of thefts from ATMs in 26 countries. Seven people have been arrested and prosecutors say an eighth person involved in the crime was murdered in the Dominican Republic late last month.
The U.S. attorney in Brooklyn, Loretta Lynch, calls it "a massive 21st-century bank heist."
She says the New York cell of the global theft operation withdrew $2.8 million in cash from hacked accounts in less than a day.
Arrests began in March. There are worries more such thefts may be in store.