Smaller financial institutions have been warned to look out for attacks that aim to increase the withdrawal limit on customer payment cards for fraud purposes.
The so-called "unlimited operations," as the U.S. Secret Service calls them, can cause financial institutions to incur large dollar losses, the Federal Financial Institutions Examination Council (FFIEC) warned Wednesday.
The agency said cybercriminals are trying to access the Web-based ATM control panels used by bank employees, which are used to set the amount of money customers can withdraw, and the geographies where they can take money out.
To gain access, the cybercriminals target bank employees with phishing emails that aim to trick them into divulging their login credentials.
"When criminals obtain this information, they may use an employee's login credentials to gain access to the control panel and change the settings to permit greater or unlimited cash disbursements at ATM machines, and to change other fraud and security related controls," the FFIEC said in its advisory.
The cybercriminals then use payment card information obtained through other attacks to make withdrawals, usually on holidays and weekends when monitoring by banks is more limited. With the normal limits modified, the thefts can be fast and costly.
"The cash-out phase of the attack involves criminals organizing simultaneous withdrawals of large amounts of cash from multiple ATMs over a short time period, usually four hours to two days," the FFIEC said.
In December 2012 and January 2013, a well-planned unlimited operation used a network of people in multiple countries to withdraw funds from customers of the Bank of Muscat, based in Oman, and the National Bank of Ras Al-Khaimah PSC, also known as RAKBANK, in the United Arab Emirates.
RAKBANK suffered US$5 million in losses after 4,500 ATM withdrawals were made in 20 countries on Dec. 22, 2012. A second attack on Feb. 19 and 20 saw the Bank of Muscat lose $40 million, withdrawn by people in 20 countries in just 10 hours.
Hackers raised the withdrawal limits on the cards after breaking into prepaid Visa and MasterCard credit card processors in the U.S. and India. U.S. authorities arrested 14 people, with other arrests made in Spain and Germany.
The FFIEC advised that institutions update login credentials for such systems that manage ATM limits and implement multifactor authentication.
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