The US Department of Justice said Wednesday that it has filed criminal charges against three men believed to be central to the FIN7 hacking group.

According to indictments unsealed in federal court in Seattle, prosecutors say that Dmytro Federov, 44, Fedir Hladyr, 33, and Andrii Kolpakov, 30, hacked into "thousands of computer systems and stole millions of customer credit and debit card numbers, which the group used or sold for profit."

The suspects are believed to have hit companies across 47 states and the District of Columbia to steal "more than 15 million customer card records."

"The three Ukrainian nationals indicted today allegedly were part of a prolific hacking group that targeted American companies and citizens by stealing valuable consumer data, including personal credit card information, that they then sold on the Darknet," said Assistant Attorney General Brian Benczkowski.

The three men have been charged with 26 felony counts of conspiracy, wire fraud, hacking, and more.

Hladyr is currently in custody in Seattle, while Fedorov was arrested in Poland and Kolpakov was busted in Spain. The United States is attempting to extradite Fedorov and Kolpakov.

In a "fact sheet" distributed to reporters, the DOJ called FIN7 "one of the most sophisticated and aggressive malware schemes in recent times, consisting of dozens of talented hackers located overseas."

FireEye released a lengthy blog post on Wednesday. In it, the cybersecurity company describes FIN7 as "one of the most prolific financial threat groups of this decade, having carefully crafted attacks targeted at more than 100 organizations."