Sounding alarm over a sinister new wave of cybercriminals, regulators are warning bankers that hackers have succeeded in changing the controls on automated teller machines to enable thieves to make nearly unlimited withdrawals using fraudulent debit, prepaid and ATM cards.

The hackers often schedule the withdrawals for holidays and weekends, when extra cash is loaded into ATMs and monitoring by the banks drops off, an umbrella group for financial regulators said Wednesday.

The U.S. Secret Service calls this scam Unlimited Operations because it eradicates the usual caps on ATM withdrawals, enabling the criminals to extract far more than depositors have in their accounts.

“A recent Unlimited Operations attack netted over $40 million in fraud using only 12 debit card accounts,” the Federal Financial Institutions Examination Council said in its alert.

— Los Angeles Times