Israel is refusing to extradite a militant Zionist hacker who has declared war on antisemitism in France.

French-born Gregory Chelli, who goes by the online moniker Ulcan, is the subject of an international arrest warrant — but Israel is not bowing to pressure from France, a stance which even prompted a visit by the French foreign minister.

The 34-year-old is the subject of a film called The Patriot, which recently took part in the DocAviv Festival in Tel Aviv and will soon air on Israeli TV. But the French language film will not be aired in France, according to Haaretz.

Despite facing 50 criminal charges, Mr Chelli still agreed to give the Israeli newspaper an interview from Ashdod, his home since making aliyah.

Directed by Daniel Sivan, the film shows how Mr Chelli waged a one-man online war on the rise of antisemitism in his homeland. Born and raised in a middle class suburb of Paris, he grew up in a family without strong connections to either religion or Israel.

All that changed about a decade ago as antisemitism grew in France and he became active in the Jewish Defence League.

“It used to be, years ago, that antisemitism was confined to the old-style extreme-rightists whom no one thought of as a sane group. But for some years now, antisemitism has become fashionable, with different, newer explanations given for it,” Mr Chelli told Haaretz.

Above all, there was the surging popularity of French comedian Dieudonné M’bala M’bala, inventor of the quenelle, the inverted Nazi salute.

“Everyone whose ideology included a Jew-hating side identified with Dieudonné and expressed support, even if they came from opposite sides of the barricade.”

With a fascination for computer programming, a young Mr Chelli taught himself to hack into websites. And so, driven by his anger over the rise of anti-Jewish hatred, he put his skills into action. He broke into Dieudonné’s official website and sent a list of his 10,000 supporters to the press — which they duly published.

Since then he has brought down websites and exposed criminals and unacceptable behaviour by posting details of them publicly.

“Nobody respects the Jews when they complain through the accepted channels. The police force doesn’t work, and therefore I took it upon myself to be the police force of the internet,” he said.

Yet some feel his acts of vengeance have gone too far. On one occasion he contacted the blind mother-in-law of far-right journalist and writer Alain Soral to tell her he had died.

“Thanks to the things I did he lost credibility and support, he lost the righteous halo that surrounded him. It’s true that it’s an ugly thing to cause distress to his wife’s old and blind mother, but I wouldn’t have done it if he hadn’t suggested loading Jews onto trains. That’s the ugliest and worst thing I’ve done,” Mr Chelli told Haaretz.

However, some argue there was worse to come.

At the height of the film, he threatens journalist Benoit Le Corre, who published an unflattering article about him. After contacting Mr Le Corre’s parents and informing them their son had died, he summoned police to their home in the middle of the night. Five days later, Mr Le Corre’s father suffered a fatal heart attack.

After years of turning a blind eye, police began to began to investigate Mr Chelli. He was accused of deliberate violence that caused death, and an international warrant was issued for his arrest.

When questioned over the incident, he said: “He published lies about me and I asked him to correct them. He knows how I operate and he contacted his parents and warned them.

“Le Corre turned the run-in with me into the reason for his father’s death, but his father suffered a heart attack five days after the conversation with me.”

Mr Chelli insisted he has since toned things down. “Today, I don’t do those things any more. I no longer call the police, because I’m afraid that a bullet could be discharged and hit someone, and for the past three years, I have not hacked anti-Israeli websites.”

The Patriot will not be screened in France as film-makers were told it is illegal to show antisemitic symbols such as swastikas and quenelle salutes.

Director Daniel Sivan told Haaretz: “A lot of the money goes to finance films that are critical of injustices the world over. They’re happy to pay for films with penetrating criticism of the Israeli occupation, for example, but they aren’t willing to see what’s happening in their own home.”