There are your everyday ATM skimming schemes, and then there are global hacking operations that allegedly siphoned $45 million from ATMs around the globe in just a few hours. It’s kind of like a flash mob, said one former prosecutor, and the ease with which it was apparently carried out has got those in the security world a little bit nervous.

So far seven people have been arrested in the U.S., reports the Associated Press, and stand accused of being the New York cell of a worldwide crime network. Authorities say thefts went down at ATMs in 27 countries from Canada to Russia, and it took law enforcement agencies from around the globe to pull off 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,” a former federal prosecutor and regional director for the U.S. Securities and Exchange Commission explains. “I expect there will be many more” of these types of crimes, she added.

The good news is that no consumers apparently lost their cash, as the hackers pulled the money from the stashes banks have to back up pre-paid debit cards, and not individual or business accounts.

According to the authorities, hackers worked their way into bank databases and erased withdrawal limits on pre-paid debit cards and made up their own access codes. Then that data would be loaded onto any old plastic card with a magnetic stripe, even a hotel key card could work.

From then on it was an old-fashioned heist, with operatives spread around the world pulling out money in multiple cities, who would then take their cuts, and then launder the rest by buying expensive goods or shipping it to the head honchos in charge of the operation.

It almost seems like the group held a trial run first, with an attack in December that stole $5 million worldwide, and then the other in February that brought in the big haul of $40 million in 10 hours, with a whopping 36,000 transactions.

The weak spot the thieves exploited seems to be the magnetic strips on the back of the cards — most of the world has ditched those cards in favor of ones with built-in chips that are a lot harder to copy. Since U.S. banks still use them, however, merchants still accept them worldwide.

Global Network of Hackers Steal $45 Million From ATMs [Associated Press]

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