PARIS (AP) — Europol says five key suspects have been arrested in connection with a massive operation aimed at knocking out a cybercrime group accused of inflicting hundreds of millions of euros in losses worldwide.

The European Union police agency said Thursday the sweep was "unprecedented in its scale" and resulted in the seizure of 39 servers and hundreds of thousands of internet domains used by the group, nicknamed Avalanche.

Unlike some past seizures — which grabbed cybercriminals' infrastructure while leaving the masterminds free to reorganize their networks later — officials say they're confident they've struck a fatal blow this time around.

"We have arrested the top, the head of the snake," Fernando Ruiz, the head of operations at Europol's Cybercrime Center, told The Associated Press ahead of the announcement. "We are sure that this will have a very huge impact."

Ruiz said the arrests were made Wednesday following months of preparation and years of investigation by law enforcement agencies from 30 different jurisdictions. He declined to say where the suspects were detained, saying the countries where the arrests took place had asked Europol not to identify them.

Senior European justice official Michele Coninsx said Thursday that the bust "marks a significant moment in the fight against serious organized cybercrime."