The sophisticated scam involved the manipulation of legitimate electronic trading platforms licensed to foreign exchange brokers, who then provided the software to their clients, the Australian Federal Police (AFP) said.

The US Secret Service in August notified authorities about the Australian links to the predominantly US-based scam, AFP said.

The accused were residents of Sydney but most victims were based in the US.

Investigations into potential Australian victims were ongoing.

The organised crime syndicate employed a mix of social engineering techniques, including messaging platforms and dating and job websites, to gain victims’ trust before mentioning investment opportunities.

The victims were directed to both fraudulent and legitimate investment applications that dealt in foreign exchange and cryptocurrency, which were manipulated to show a false positive return on investments.

After victims became subscribers to an investment service, data was changed to encourage further investment, while concealing the fact their money had been stolen.

AFP detective sergeant Salam Zreika said in a statement the case highlighted the need to “refrain from investing in foreign exchange, crypto-currency, or speculative investments with people you have only ever encountered in the online environment.”

The four arrested men registered Australian companies to make their scams look genuine, and created Australian business bank accounts to launder the proceeds, police alleged.