Estonia

Two Estonian citizens, Sergei Potapenko and Ivan Turõgin, have pleaded guilty to defrauding $577 million in the HashFlare Ponzi scheme, promising cryptocurrency mining but actually lacking the computing power to deliver as promised.
Sophisticated Crypto Investment Scam
#HashFlare advertised as a cloud cryptocurrency mining service, attracting over $577 million from investors from 2015 to 2019.
In reality, the company did not have enough mining equipment, used fake data to create the illusion of phantom profits, and defrauded investors.