Two Nigerians are in trouble in the United States after being indicted by prosecutors for running a fraudulent bitcoin investment scheme.

The Nigerians, Onwuemerie Ogor Gift and Kelvin Usifoh, were charged by Oregon District Attorney’s Office with 11 counts of wire fraud, as well as conspiracy to commit wire fraud and money laundering, according to a report.

From December 2017 to June 2018, Gift and Usifoh allegedly promoted the fake bitcoin investment scheme via three websites – wealthcurrency.com, boomcurrency.com and merrycurrency.com – promising investors 20–50 percent risk-free returns with instant withdrawals.

Gift and Usifoh falsely claimed that victims’ bitcoins would be invested using “unique trading methods” and that they would maintain a “constant high interest rate.” The pair also allegedly encouraged investors to transfer bitcoin to their own cryptocurrency wallets. Once transferred, Gift and Usifoh would exchange it for Nigerian naira.

In over six months, the defendants stole 10.88 bitcoins (worth approximately $56,391 at press time) from three victims, one residing in Oregon and two in California, according to the indictment. They also used a photo of a fourth victim to promote their scheme.

In total, the prosecutors alleged that Gift and Usifoh received more than 50 bitcoins ($259,000) through the scam.

Largely due to their pseudonymous, online nature, cryptocurrencies are becoming increasingly popular as a means to scam investors. But law enforcement is catching up.

Last month, New York prosecutors charged a man in a nine-count indictment for duping investors out of over $200,000 in cryptocurrency and cash. And, in February, a 20-year-old man was indicted in the New York Supreme Court over SIM-swapping identity and crypto theft.

Warning cryptocurrency investors over such schemes, the U.S. Securities and Exchange Commission and the Commodity Futures Trading Commission jointly issued an alert earlier this week, saying that claims such as “risk-free”, “absolutely safe” and “guaranteed profit” are hallmarks of a fraud.