Algerian Hamza Bendelladj has been extradited back to the US to face charges that he used a virus to steal money from more than 250 banks.
The 24-year-old, who was arrested in Thailand at the turn of the year, is accused of co-creating the SpyEye malware.
The program obtains log-in data for online bank accounts.
A guilty verdict could see Bendelladj sentenced to more than 30 years in prison and fined £9 million.
In a statement, US attorney Sally Yates said: "Bendelladj's alleged criminal reach extended across international borders, directly into victims' homes.
"In a cyber-netherworld, he allegedly commercialised the wholesale theft of financial and personal information through this virus which he sold to other cybercriminals."
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