A visual representation of the digital cryptocurrency bitcoin in London, Oct. 23, 2017. Dan Kitwood/Getty Images

South Korean authorities on Wednesday indicted over two dozen people associated with a cryptocurrency operation for their involvement in a multimillion dollar scam. The large-scale fraud scheme was being run by Mining Max, a cryptocurrency mining company headquartered in Las Vegas.

The suspects, which include the company’s chairman and vice chairman, as well as a Korean singer popular in the 1990s, are accused of embezzling about $250 million from 18,000 investors in 54 countries, including the United States, South Korea, China and Japan, Yonhap News Agency reported.

Of all the suspects, 21 were indicted by the Incheon District Prosecutors’ Office on charges of fraud and for violating the country’s law on door-to-door sales. Mining Max has a cryptocurrency mining farm in Seoul, and promises investors profits from its high-tech mining facility. Since the company was mining currency from different blockchains, it purportedly gave investors the option to choose to mine the currency that offered them the best returns.

The company actually worked like a pyramid scheme, requiring people to pay to become an affiliate and rewarding them for getting others to sign up. Its complex structure for returns on your investment (not unusual for such a business model) is explained on this website, which was only one of many that, months ago, was questioning the legitimacy of Mining Max.

Other than the 21 people, three others associated with the company — including Korean singer Park Jung-woon — were indicted on embezzlement charges but were not detained. Seven others, including company chairman Daniel Park, the vice chairman, and some top investors, are on the run and have been put on an Interpol wanted list.

The company’s scam began to come undone when it couldn’t make enough returns from its cryptocurrency mining to keep giving money to lower-level investors. The top investors were paid part of the scam proceeds, as well as other luxury items like expensive cars and watches, Yonhap reported.

Prosecutors also believe only about $80 million of the investors' money was spent on buying equipment to mine cryptocurrency (mostly Ethereum, currently the second-most popular cryptocurrency after Bitcoin), with the rest of it being used by the management for personal enrichment or to reward the top investors. About $110 million is thought to have been stashed in offshore bank accounts.

Most of the 18,000 victims of Mining Max, about 14,000, are from South Korea, while 2,600 are from the U.S. China accounts for another 600 people affected by the scam, and the remaining come from other countries, including Japan.