With secret codes and locked-down communication, Swedish publisher Norstedts has kept the plot of the sequel to the best-selling Millennium crime trilogy, due out on Thursday, shrouded in secrecy.

The mystery is fitting for the sci-fi spy intrigue entitled The Girl in the Spider's Web, the highly-anticipated dark thriller penned 11 years after the death of the series' creator Stieg Larsson.

Only a few people have read the 500-page tome - just translators and editors - that takes up the story of tattooed computer hacker Lisbeth Salander and journalist Mikael Blomkvist.

And Norstedts has given fans only a small sneak preview.

"One night professor Frans Balder, a leading authority within AI (artificial intelligence) research, calls up Blomkvist," it wrote on its website.

"Balder says he has world shattering information on US intelligence services. He has also had contact with a female super hacker, who bears a certain resemblance to a person Blomkvist knows well."

The thriller is keenly awaited by devoted readers. The first three Millennium books, published in 2005-2007, have sold 80 million copies worldwide and have been made into Swedish and Hollywood movie adaptations.

But before the fourth installment even went to press it was already enveloped in scandal.

Among the book's detractors is Eva Gabrielsson, who was Stieg Larsson's partner of 32 years until he died suddenly of a heart attack in 2004 at age 50.

The couple were not married and Larsson left no will, so his estate went to his brother and father. Gabrielsson, 61, lost a bitter battle with them to manage his work.

To write the trilogy's sequel, Larsson's brother and father chose David Lagercrantz - a Swedish journalist known for writing soccer star Zlatan Ibrahimovic's official biography - a "totally idiotic choice," Gabrielsson told AFP in February, saying he knew nothing of the milieu Stieg Larsson described in the books.

Around 2.7 million copies go on sale in 25 countries on Thursday, and in the US on September 1.

AFP