Factual error: The whole book is about a computer breaking a very strong code, and that for every code a large enough computer can be built to break it. That's simply not true: The "one time pad" cannot be broken by brute force, only by traditional stealing of the key.
Factual error: The director in the story, Leland Fontaine, is a civilian, and we are told that he worked his way up through the ranks of the NSA. However, this would not occur in real life, as since the NSA was founded, the director has always been a military officer of three star rank.
Factual error: Towards the end of the book the protagonist is being chased up the Giralda, but manages to escape by pushing his pursuer down the stairs. There are only a few steps at the very top the Giralda, however. Most of the inside is ramped.
Factual error: The list of encryption algorithms broken includes ZIP, which is not an encryption algorithm.