The Adversary: Chris Bruen, Book 1

Former DOJ cybercrimes prosecutor Chris Bruen walks into a dark apartment in Amsterdam to confront a hacker known as Black Vector. The hacker has stolen the source code for the world's most ubiquitous operating system, which powers everything from personal computers to the NSA's data centers. This should have been a routine assignment for Bruen, but instead of obtaining a confession, Bruen finds the hacker's dead body and uncovers a hidden flash drive that contains the code for a remarkably sophisticated computer virus known as Lurker.