This is a really great book. If you've read any of Dan Brown's works, e.g. DaVinci Code or Angels and Demons you will not be at all surprised by the style. Digital Fortress is fast-paced and quickly switches scenes whcih collectively become more and more obviously related and intertwined as the book paces on. Again, totally Dan Brown in style.
Digital Fortress is a story about a super decoding machine created by the National Security Agency to be used for the purpose of decoding electronic messages. The machine is being manipulated and hacked presumably by an ex-employee/creator of the system itself. It's a bit difficult early on to decide which characters can be trusted. In fact, you may find yourself going back and forth with respect to your opinion of certain characters. A college professor finds himself on a mission filled with danger. He's on the trail of an ex-employee of the agency that is currently being attacked. You'll have to check out the book for more information as I don't want to spoil any of the fun. It's a great techno-thriller.