I just finished Digital Fortress. I had lot of expectations because it was a Dan Brown book. The book was a huge let down. One of my friends had told me to skip this book, but being a hard core fan of Brown I just could not skip it.
The story starts off with lovers separating for some secret assignments and ends with a the guy proposing and she agreeing. And they lived happily ever after. There is a mystery agency in the US which spies on all the messages which the terrorist groups etc exchange. A guy fools this agency and introduces a virus into the agency's decoding machine. There is lot of turns and twists in the story line but there is no clear villain. Finally the agency is rescued by the hero and the heroin. Both guess the secret pass code to break the virus at the same time (which happens to be the last second before USA is otherwise destroyed in typical filmi istyle).
The story drags a bit in the middle, but the last 30 pages or so is super and you cannot keep the book down without completing.
There are some typical features of Brown in the novel. Some anagrams, some ancient code breaking techniques, origin of words etc. These are interesting.