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International crime rings targeting California's booming agriculture industry are increasingly stealing truckloads of high-value nuts, prompting authorities and the firms falling victim to ramp up efforts to break the spree costing millions.

The sophisticated organizations in many cases use high-tech tactics, hacking into trucking companies to steal their identity. Armed with false shipping papers, they pose as legitimate truckers, driving off with loads of nuts such as almonds, walnuts or pistachios valued at $150,000, and some worth $500,000 each.

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Days later, when a shipment fails to arrive to its intended destination, the nuts may already be in another state or on a ship destined for Europe or Asia, where they fetch top dollar on the black market, authorities say.

Last year, nut thefts hit an all-time high in California — with losses totaling $4.6 million from 31 reported cases, more than the three previous years combined, according to CargoNet, an alliance of cargo shipping firms and law enforcement agencies aimed at preventing losses.

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Losses for all four years combined were nearly $7.6 million, the group reports.

"It's made my life miserable," said Todd Crosswell, general manager of Caro Nut Co.

Caro was victimized six times last year for a total loss of $1.2 million. In each case, thieves stole cashews imported from Vietnam and Africa that were roasted, salted and packaged in Fresno.

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The value of nuts grown and processed in California, the nation's leading agricultural state, have soared in recent years as global demand for the health-food snack grows in places such as China and emerging economies.

California produces more almonds, walnuts and pistachios than any other state with a combined value of $9.3 billion in 2014. Almonds alone were valued at $5.9 billion, according to the U.S. Department of Agriculture.

The high value of nuts grabbed the attention of criminal organizations, who are exploiting weaknesses in the cargo shipping industry to reap big profits, said Dan Bryant, supervisory special agent for the violent and organized crimes programs of the FBI Sacramento office.