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The book

INVISIBLE ENEMY

The true story of cybercrime in Denmark. About hackers, ransoms, data hostage negotiators and the human fates behind the attacks.

Available in Danish & English

Invisible Enemy – book cover

What is the book about?

A new kind of war

Invisible Enemy is a character-driven, cinematic account of the new digital power and the new vulnerability. It follows Jan Kaastrup, cyber investigation leader, and Michael Sjøberg, data hostage negotiator, through real cases involving Russian hacker gangs, million-dollar demands and companies on the brink of bankruptcy.

Behind the technical jargon live real people with everything to lose. The book tells the story of Rosendahl Design Group waking up to a ransomware attack. Of Conti — Russia's most dominant hacker group. Of municipalities paying millions in ransom. And of the people who fight back.

Journalist Ida Nyegård Espersen spent ten months at Jan Kaastrup's kitchen table and created a book that makes the cyber threat tangible for everyone, not just IT professionals.

Language
Danish & English
Kapitler
13 kapitler + Prolog

What the press say

PRESS REVIEWS

"Invisible Enemy is as gripping as a crime novel — takes us into the engine room and tells the story of ransomware, ransom negotiations and the fragility of our digital society."
Altinget, Mille Østerlund, 16 February 2026
Information

"A well-written and accessible account of the history of hacking and cybercrime."

— Peter Christian Bech-Nielsen, Information, 4 February 2026

Bogblogger.dk

"An outstanding, gripping and well-told book. We are taken deep into the engine room and gain insight into the catastrophic consequences of a hacker attack."

— Morten Kidal, Bogblogger.dk, 9 March 2026

Weekendavisen

"Almost screaming to become a Netflix series."

— Weekendavisen

Politiken

"As gripping as a crime novel — the storytelling is absolutely top-notch."

— Politiken

Økonomisk Ugebrev

"The cases are interesting and instructive — an important book about what happens when the digital threat becomes reality."

— Ole Borch, Økonomisk Ugebrev Kultur, 18 March 2026

Bog & idé

"Two of Denmark's leading investigators of cybercrime take us deep into the engine room and provide insight into a new and frightening world."

— Bog & idé product page

Featured in

Information
Altinget
Politiken
Weekendavisen
Bogblogger.dk
Økon. Ugebrev
Saxo
Mofibo
Bog & idé

Reader response

WHAT READERS SAY

4,4
★★★★½
out of 5
70+ reader ratings
on Saxo.com — Denmark's largest book retailer
Read all reviews on Saxo →

"A book that in these times should be presented to all levels of management — if your company is connected to the internet."

Ole R.
Saxo, 15. marts 2026

"This book should be read by anyone sitting on a board or in a leadership role."

Benita Z.
Saxo, 6. marts 2026

"A must-read if you work in information security or are a risk owner."

Thomas Vinding P.
Saxo, 12. februar 2026

"Told in accessible language — how bad things can get, but also how being prepared can limit the damage."

Helen R.
Saxo, 14. marts 2026

"A good book covering the state of IT security today with excellent real-world examples."

Mille C.
Saxo, 5. februar 2026

"A frightening insight into a world most of us do not understand."

Saxo-læser
Saxo, april 2026

"A really good and enlightening book!"

Torben M.
Saxo, 4. marts 2026

"Good and insightful."

Saxo-læser
Saxo, marts 2026

"A truly interesting book."

Jan Teddy J.
Saxo, 11. april 2026

Who reads it?

Readers highlight the book's ability to make complex cyber threats understandable through real cases. A recurring theme is the combination of technology, psychology and negotiation technique. The book is particularly recommended for:

Boards of directors CEOs & executives IT & security managers Risk owners Public authorities Anyone interested in modern crime

Contents

Chapter overview

Chapter 1
The Hacker and the Hostage Negotiator

Two Danish boys grow up amid the optimism of the 90s and each find their way into a digital world without borders.

Chapter 2
The Extortion Case

A business owner receives a message no one wants to receive. The money rolls, but the question is who wins.

Chapter 3
The Two Gazes

Jan and Michael view cybercrime from two different perspectives. Eventually they meet.

Chapter 4
The Poker Case

Bluff, threats and a criminal network that knows exactly what it is doing.

Chapter 5
New Masters of Power

Hacker gangs organise themselves like companies with support, HR and KPIs.

Chapter 6
Payment or Destruction

Rosendahl Design Group wakes up to threats and a ransomware attack.

Chapter 7
A Way to Freedom

Behind the encryption hides a human being. Or does it?

Chapter 8
The Hackers Get Hacked

The rules of the game are turned upside down.

Chapter 9
Alone Through the Forest

A helper must be evacuated from Ukraine.

Chapter 10
From Akira with Love

A new hacker group introduces itself in the hardest way.

Chapter 11
A Municipality Pays its Hostage-Takers

Public authority, million-dollar bill and a secret that cannot be kept.

Chapter 12
The King of Cash

The money must be laundered. Who helps?

Chapter 13
You Mean Putin, Right?

The link between Russian state power and the criminal hacker groups.

Excerpt

From the Prologue

The text message from Jan was brief: "Call".

Michael received the message on Saturday 5 February 2022 at 9.18am. Although Jan's text consisted of just four letters, Michael sensed that his response to it would lead to extensive work — and Michael was due at an orientation meeting at his son's new school at 10. He called Jan anyway. Too curious not to.

"Hi Michael. Good that you called. There's a new case. Jesper's company has been hit."

"Uh, do we know who the hackers are?" asked Michael.

"It's bloody Conti," Jan replied.

Michael felt chills rolling down first his arms and then his thighs when he heard the name Conti: "Fuck," he exclaimed. "Yes, this is serious," said Jan. Children were screaming in the background.

Book a lecture Contact the authors

FAQ

QUESTIONS ABOUT THE BOOK

Is the book available in English?

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Where can I buy the Danish edition?

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Is the audiobook available in English?

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Can I buy multiple copies for my company?

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Who has written the book?

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For companies

ORDER FOR YOUR ORGANISATION

Order copies of Invisible Enemy for your employees, board members or as gifts. Available in Danish and English, with or without personal dedication.

  • ✓Invoiced after delivery. No advance payment required.
  • ✓Available in Danish and English, or a mix of both.
  • ✓Personal dedication from the authors on request.
  • ✓Bulk discount on larger orders. Contact us.
  • ✓Can be combined with a lecture.

Buying for yourself?

The Danish edition is available on Saxo, Mofibo, Storytel and Spotify. The English edition can be pre-ordered below.

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