Card skimmers have been around for a while. And while they may have gotten smaller and harder to detect, the people using the skimmed data were generally limited to how much cash they could pull out of victim’s accounts in a day. And so a new breed of criminal has figured out a way to steal hundreds of thousands of dollars from ATMs.

The Minneapolis Star-Tribune obtained a letter sent from Visa to clients warning them that some bad people have gotten around some of the limits put on ATM cash withdrawals.

“In a recently reported case, criminals used a small number of cards to conduct 1000’s of ATM withdrawals in multiple countries around the world in one weekend,” reads the letter, which explains that the perpetrators are “gaining access to issuer authorization systems and card parameter information” with the goal of using individual ATM cards to “facilitate massive fraud.”

And they don’t mean a few hundred bucks.

“In some instances over $500K USD has been withdrawn on a single card in less than 24 hours,” writes Visa.

Meanwhile, the folks at FICO recently sent out an alert regarding the arrest of four men in New York and New Jersey accused of making illegal ATM withdrawals. But these weren’t your regular scammers, as both the Secret Service and Homeland Security were involved.

The person who manages FICO’s Card Alert Service tells the Star-Tribune that his company’s alert was tied to the Visa notice and both notices were in regard to malware attacks aimed at retailers. The hackers “may have accessed or penetrated the point-of-sale systems for a couple of merchants in the U.S.”

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