New York, for example, members of the cell fanned out into the city on the afternoon of February 19, armed with cards bearing a single Bank of Muscat account number. Ten hours later, they had completed 2,904 withdrawals for $2.4 million in all, the final transaction coming around 1:26 a.m., prosecutors said.
Casher crews in other countries were busy doing the same, pulling some $40 million from Bank of Muscat to add to the $5 million they stole from RAKBANK in December, according to the indictment. In total, cashers made some 40,500 withdrawals in 27 countries during the two coordinated incidents.
Prosecutors said the method of attack was known as "Unlimited Operations" in the cyber underworld.
Representatives for the two banks could not be reached for comment outside of regular business hours.
In a statement, Mastercard said it had cooperated with law enforcement in the investigation and stressed that its systems were not involved or compromised in the attacks.
In late February, Bank Muscat disclosed that it would take an impairment charge of up to 15 million rials because it had been defrauded overseas by 12 prepaid debit cards used for travel. That charge was equal to more than half of the 25 million rials profit it posted in its first quarter ended March 31.
HIGHLY SKILLED HACKERS
Cyber experts said they believe the operation likely required the work of several hundred people, at least several of whom were highly skilled hackers capable of devising ways to penetrate well-protected financial systems.
"Hackers only need to find one vulnerability to cause millions of dollars of damage," said Mark Rasch, a former federal cyber crimes prosecutor, based in Bethesda, Maryland.
The group may have targeted Middle Eastern banks because they tend to allow customers to put much larger sums on cards and do not monitor them as closely as banks in other regions, said Shane Shook, global vice president of consulting for the security firm Cylance Inc.
"It's a target-rich environment in terms of soft electronic security," said Shook, an Arabic speaker who has spent more than a decade investigating cyber crimes.
The case is similar to one in 2009 that targeted the