OneCoin has been called "one of the largest international frauds ever" in the United States, with about 3 million investors defrauded of more than $4 billion (about 27.9 billion yuan).

Karl Sebastian Greenwood, co-founder of the multibillion-dollar cryptocurrency platform OneCoin, has pleaded guilty to multiple charges brought by the U.S. Department of Justice (DOJ) and faces up to 60 years in prison.

OneCoin, a Bulgarian company co-founded by Greenwood with "crypto queen" Ruja Ignatova, sells a cryptocurrency of the same name. Emails between the two men, obtained by the U.S. Justice Department before Bitcoin was founded in 2014, found that they called it a "junk token."

On the surface, OneCoin claims to be a multi-level marketing company whose members earn commissions by selling and mining more cryptocurrencies that include OneCoin. OneCoin can only be exchanged for fiat currency on private Xcoinx exchanges.

In effect, it is a pyramid scheme, i.e. a Ponzi scheme, because investors can recruit others to join the scheme without the actual product, while later investors use the money of earlier investors to make a profit.

According to the U.S. Department of Justice, Greenwood earned about $21.2 million per month as a "global master distributor" for cryptocurrency scam companies.

Greenwood is scheduled to be sentenced before District Judge Edgardo Ramos on April 5, 2023.

U.S. Attorney Damian Williams said Greenwood's guilty plea "sends a clear message" that the Justice Department is "going after all those who attempt to commit fraud by exploiting the cryptocurrency ecosystem, no matter how big or sophisticated you are."

In June, Greenwood's partner Ignatova, the "Crypto Queen," was placed on the FBI's Ten Most Wanted list for his role in the scam. She is still on the run and was last seen travelling to Athens, Greece, in October 2017.

Authorities elsewhere have indicted people linked to OneCoin and Ignatova, and three of their associates face charges of fraud and money laundering in Germany.