Two Estonian nationals were sentenced on Tuesday in Washington state to 16 months in prison for carrying out a cryptocurrency Ponzi scheme that netted more than a half-billion dollars.

Sergei Potapenko and Ivan Turõgin, both 40, worked alongside four unnamed co-conspirators to defraud investors through a bogus cryptomining operation, the Department of Justice said in a statement Tuesday.

According to court documents, around 2013 they created the company HashCoins, which advertised the sale of mining equipment for bitcoin and other virtual currencies. Orders poured in from customers but HashCoins didn’t actually make mining equipment. Instead it purchased and assembled mining equipment from other companies, but at no point did it have sufficient inventory to deliver what it had promised to customers. 

Faced with a growing number of complaints from customers, Potapenko and Turõgin pivoted to advertising “remote” mining services whereby investors would receive a percentage of profits from a pooled mining operation they called HashFlare. Investors were able to see their purported earnings on an online dashboard but ran into roadblocks when they attempted to cash out. In reality, according to court documents, HashFlare only had 1% of the computational power for mining bitcoin that it had sold to customers, and 3% of the bandwidth for mining altcoins. 

Potapenko and Turõgin have already served 16 months in prison and will return to Estonia for supervised release. The U.S. and foreign law enforcement partners seized assets — including cryptocurrency and cash, vehicles, real estate and cryptocurrency mining equipment — valued at over $450 million from the men. The forfeited property will be used to compensate some of the hundreds of thousands of victims worldwide. 

According to a release, prosecutors had argued for a 10-year prison stint and the Justice Department is considering appealing the sentence.