The Girl in The Spiders Web by David Lagercrantz (Millennium #4)

The girl with the dragon tattoo is back.
Lisbeth Salander and Mikael Blomkvist have not been in touch for some time.
Blomkvist is contacted by renowned scientist Professer Balder. Fearing for his life, but more concerned for his son's well-being, Balder wants to publish his story. But more interesting to Blomkvist is Balder's connection with a certain female superhacker.
It seems that Lisbeth Salander, like Balder, is a target of a gang of ruthless cyber criminals which soon bring terror to the streets of Stockholm, to the Millennium team, and to Blomkvist and Salander themselves.