A Russian goes on trial in Paris Monday accused of having defrauded nearly 200 victims across the world of 135 million euros using ransomware.
Prosecutors say Alexander Vinnik sent emails to his targets masquerading as invoices, whose attached document, when opened, activated malware that shut down the computer and encrypted its contents.
A message would appear on the hacked computer with instructions to pay a ransom in the online currency Bitcoin to regain control of the machine.
Among the 188 victims of the attacks -- which happened between 2016 and 2018 -- were local authorities, businesses and individuals across the world.
In France, many of the victims were local councils, law or insurance firms and small local businesses such as driving schools or pharmacies.
Vinnik, who has denied charges of extortion and money laundering, has refused to answer questions put by investigating magistrates.
He is also wanted in both the United States and his native Russia.
Investigators described the system he allegedly used as extremely elaborate, involving the mass mail-shots of the "contaminated" emails via a botnet: a network of already infected computers.
The way that the paid ransoms were subsequently laundered to make it difficult to trace was equally sophisticated, says the indictment.
Prosecutors identified 20 businesses in six cities across France among the victims and following the money trail through various bank accounts -- as much as $8 million -- identified one as belonging to Vinnik.
US investigators suspect the 41-year-old of being the mastermind of what they say has become one the main ways cybercriminals launder their illegal gains.
Vinnik was extradited to France in January from Greece, where he had been arrested on an American warrant in 2017.
He allegedly operated the BTC-e bitcoin exchange until his arrest at the northern Greek tourist resort of Halkidiki, which set off a three-way extradition tussle between the United States, France and Russia.
Greece eventually preferred the European warrant issued by France.
A US indictment accuses Vinnik of 21 charges ranging from identity theft and facilitating drug trafficking to money laundering.
He tried unsuccessfully to be extradited to Russia, where he is wanted on lesser fraud charges involving just 9,500 euros ($11,000).