He participated in a France 2 television program called "Complément d'enquête" (Further investigation), and he said - and demonstrated - that he has gained access to computers belonging to the French Army and Thales Group, a French company that provides information systems and services for the aerospace, defense, and security markets.
He also said he sells and uses credit card and bank account data to buy himself and others various things.
Such claims could not have gone unnoticed, and Thales took immediate measures. It said that he had stolen confidential information from its networks and asked for a formal investigation.
How the French police tracked down the hacker - who was presented as "Carl" during the television programme - is unknown.
The producers of the program say that they respect the anonymity of their sources and that they haven't shared his identity with the police. In fact, they claim they did not know that an investigation was ongoing.
They also say that they were denied any information when they asked the police for it, and that they have learned everything they know from the Agence France-Presse.
"Carl" was arrested on April 7 in Paris. The police discovered on his computer a great number of compromised credit card and bank account data.
Softpedia reports that he remains in custody until the hearing, and he's facing a various set of charges: unauthorized access, data theft, and organized fraud.
The interesting thing is that the program was actually focusing on the new type of hacker - the hacktivist, and "Carl" claimed he was a member of Anonymous. Whether that's true is hard to determine since there is no list of Anonymous members. The group is not called Anonymous for nothing.