Rui Pinto, the Portuguese hacker linked to the Football Leaks whistleblower website, made his first appearance before a Lisbon judge on Friday.
The 30-year-old who was arrested in Hungary on 16 January and extradited to Portugal on Thursday, faces charges of data theft and attempted extortion.
The appearance on Friday was to allow the judge to decide what judicial measure to apply.
Pinto's lawyer Francisco Teixeira da Mota would not say if his client intended to answer questions from the judge or remain silent.
Pinto is suspected of hacking Sporting, a Lisbon football club, and Doyen Sports, an investment fund based in Malta. He is accused of asking Doyen for as much as 1 million euros ($1.13m) to stop him publishing compromising documents on the internet.
He faces up to 10 years in prison.
His lawyers argue that Pinto is a "very important European whistleblower."
Staring in 2015, Pinto hacked millions of files in order, he said, to reveal the football industry's "dishonesty".
In 2016, he shared four terabytes of data with a European media consortium which then published the Football Leaks, revealing tax evasion, possible fraud and corruption involving star players and big leaders.
Pinto said when he was arrested in Budapest he had six more terabytes of unpublished document. According to the Portuguese press, the Hungarian authorities passed that data on to Portugal.
"I was collaborating with the French authorities, starting a collaboration with Swiss authorities and probably to start another European collaboration, and suddenly Portugal sabotaged everything," he said.
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