The sophistication of a global network of thieves who drained cash machines around the globe of an astonishing $45 million in mere hours sent ripples through the security world, not merely for the size of the operation and ease with which it was carried out, but also for the threat that more such thefts may be in store. Seven people were arrested in the U.S., accused of operating the New York cell of what prosecutors said was a network that carried out thefts at ATMs in 27 countries from Canada to Russia. Law enforcement agencies from more than a dozen nations were involved in the investigation. “Unfortunately these types of cybercrimes involving ATMs, where you’ve got a flash mob going out across the globe, are becoming more and more common,” said Rose Romero, a former federal prosecutor and regional director for the U.S. Securities and Exchange Commission. Hackers got into bank databases, eliminated withdrawal limits on pre-paid debit cards and created access codes.