Seven people have been charged in New York over the heist, which allegedly stretched across 26 countries.
An eighth suspect is thought to have been murdered in April.
The network used fake cards to target banks in the United Arab Emirates and Oman, court documents said.
Prosecutors said law enforcement agencies in Japan, Canada, the UK, Romania and 12 other countries were involved in the investigation.
Arrests had been made in other countries, they said, although details were not released. 'Laptops not guns'
"The defendants and their co-conspirators participated in a massive 21st Century bank heist that reached across the internet and stretched around the globe," Loretta Lynch, US Attorney for the Eastern District of New York, said in a statement.
Prosecutors believe the group broke into the Bank of Muscat based in Oman in February. In the space of 10 hours, cashier cells withdrew $40m from ATMs.
According to the indictment of the New York defendants, they quickly moved to launder their cash, opening a Miami bank account and pouring money into cars, including a Porsche and a Mercedes, and Rolex watches.
Seven people have been arrested and face charges of conspiracy to commit access device fraud and money laundering.
The accused ringleader of the cell was reportedly murdered in the Dominican Republic just weeks earlier, prosecutors said.
"Our message is clear. Law enforcement should not stand by as cyber criminals target our global financial system for their own ends," Ms Lynch told reporters.
She added that the attack was the "largest theft of this type that we have yet seen".