Stockholm - The tattooed young hacker Lisbeth Salander is back in the sequel to Stieg Larson's Millennium trilogy but with a twist - a new author and a contemporary backdrop that includes spies from the United States National Security Agency (NSA).

The books by Larson, who died in 2004, have sold more than 80 million copies in 50 countries.

Salander was made famous in the first, The Girl With The Dragon Tattoo, which was made into a 2011 film with Daniel Craig and Rooney Mara.

Swedish author David Lagercrantz, known for his autobiography of Swedish football star Zlatan Ibrahimovic, I Am Zlatan, was tasked with writing the fourth book and there are already plans to make the sequel into a movie.

"I was terrified, but that made me a better writer," he told a news conference.

"I understood that if I turned down this (offer), I would regret it for the rest of my life. It's like meeting the woman of your life."

The Girl In The Spider's Web, released in 25 countries yesterday, has already been translated into 42 languages. The first edition will be 2.7 million copies.

To keep anyone from hacking the manuscript, Lagercrantz wrote on a computer that was not connected to the Internet. People involved in its production used code words to discuss it.

The plot reunites Swedish journalist Mikael Blomkvist and Salander, who this time is involved in a murky world of cyber security and artificial intelligence.

"It struck me that if Lisbeth would have a worthy opponent, it would be NSA," Lagercrantz said. "We live in a world where we need Lisbeth Salander more than ever."

The book has sparked controversy in Sweden, with two childhood friends of Larsson calling the publication a "grave robbery".

The first book in Larsson's trilogy was published in mid-2005.

The Swedish title, Men Who Hate Women, became The Girl With The Dragon Tattoo when it was later published in English.

The Girl Who Played With Fire and The Girl Who Kicked The Hornets' Nest completed the best-selling trilogy.

REUTERS