The pair, according to German police, used nothing more than perseverance and simple invasive programmes called Trojans, which can break into private computer networks. But they are alleged to have hacked into the computers of a string of world famous stars and downloaded hundreds of documents including music, credit card details, emails and photographs.

Their haul included a picture of the American singer Kesha, reportedly naked and having sex. Prosecutors said that the two had tried to blackmail the 24-year-old singer, but no money changed hands.

Happy with their success, the duo allegedly bragged on internet forums about their ability to hack into the computers of A-list celebrities. But prosecutors believe their main goal was unreleased musical material, which can fetch high prices on the internet. They sold some of the music they had obtained.

“Basically we are talking about illegal, bootlegged publication, and spying using Trojans,” state prosecutor Rolf Haferkamp, told the newspaper Neue Ruhr/Neuer Rhein Zeitung. “The trick itself is nothing special. All it requires is a bit of know-how and perseverance to achieve criminal success.” He added that the hacking had forced a number of singers to bring forward record release dates.

The alleged crime came to light only when fans of Kelly Clarkson, another targeted singer, tipped her off about unreleased music available on the internet. She informed the police, triggering an investigation involving the FBI and the German Federal Police Service.