The theft of hundreds of cryptocurrency miners in Iceland has led to a series of arrests amid an ongoing investigation.

The Associated Press reports that as many as 600 miners – which have yet to be recovered – were stolen during four separate incidents in December and January.

Eleven people, including a security worker, have been arrested in connection with the investigation into what has been called the “Big Bitcoin Heist.” Two of those arrested remain in custody after a Reykjanes District Court ruling, though it is unclear what role they allegedly played in the heists.

Officials in Iceland reportedly said the scheme to steal the machines, which are worth close to $2 million, is the biggest in the island nation’s history. Police commissioner Olafur Kjartannson, who works in the southwestern Reykjanes region where two of the thefts took place, said they were “on a scale unseen before.”

“Everything points to this being a highly organized crime,” he said.

Iceland boasts a long-running bitcoin mining ecosystem, thanks to the country’s data center industry and access to geothermal energy sources. In recent days, politicians there have reportedly begun exploring the idea of taxing Icelandic mining operations.

That mining hardware would be a target for larceny is perhaps unsurprising, given the growth in cryptocurrency prices in recent months. Past incidents include the theft of 165 miners from bitcoin miner BTCS at a facility in the U.S. state of North Carolina in 2016.

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