Much of the trade is in the hands of criminal gangs, known as triads.

ECONOMIST: Intellectual property

Sleeping Dogs is the story of Wei Shen, an undercover cop sent to infiltrate one of the most dangerous Triads in his native Hong Kong.

FORBES: Sleeping Dogs: Brutal Violence With a Soft Side

He said that American casinos instituted background checks, international accounting standards, and other good-faith efforts to prevent the encroachment of organized crime, but triads found inventive solutions.

NEWYORKER: The God of Gamblers

The Colombian cartels, Chinese tongs, Hong Kong triads, Japanese yakuza, and eventually after 1989 the Russian mafiya were all approached this way: first as criminal organizations, only later as traders.

NPR: Tracking the World's Black Market: 'Illicit'