“It contains more than 30 separate modules that can be tailored to the computer it’s infecting. One of the most powerful components automatically rolls back ATM transactions shortly after they’re made. As a result, people with payment cards from a compromised bank can withdraw nearly unlimited sums of money from ATMs belonging to another bank. Because the Metel module repeatedly resets card balances, the criminals never pass the threshold that would normally freeze the card. Last year, the rollback scheme caused an unnamed bank in Russia to lose millions of rubles in a single night.”
Source: Clever bank hack allowed crooks to make unlimited ATM withdrawals | Ars Technica
