A cracker (criminal hacker) is running rampant on computer systems worldwide, easily breaking strong encryption that would eons for the most powerful computers today to accomplish. The motives behind his efforts appear to be world domination. It's up to the special team of Net Force to stop him.
That's the premise for Tom Clancy's venture in the cyberpunk genre. The book is a good page turner and the characters are interesting. Though what is grating are his authoritarian views (as everyone knows, it is the rebels that have the upperhand in virtuo), and his description of the weaponry (I'm sure Freud would have a field day with it). The dialogue is poorly written and horribly amusing at times. The possibility to using quantum computing to solve NP-hard problems is interesting, as are new cryptographic systems that circumvent computing that can break existing encryption schemes.
Even with all its flaws, the basic story line is quite compelling and is reminscent of early efforts in the cyberpunk genre, particularly Web of Angels by John M. Ford (where the idea of attacking an intruder in cyberspace is accomplished by an electrical feedback to the neural interface; incidentally that book has been quoted by one reviewer as having "inspired Rucker, Sterling, and Gibson"). Worth checking out to see how a master of one pop genre (war games/high level conspiracy type of books) tackles another one.