Ross Anderson’s book “Security Engineering” is now available for free download. The idea is to make it available to people who can’t afford to buy the book; and for people who can afford the book, to let them read some of the text so that they can see it really is worth buying. (I can testify that it is beautifully printed and bound and definitely worth the money).
This is the best book on security I have come across and one of the best books on any technical subject. I recommend it to many of my friends who have no technical background at all, because it manages to convey the essence of security thinking with such a variety of interesting, well-researched examples. Although it is a serious academic book, it is accessible to people with no specialist background in mathematics or computing. Moreover, it is written in English.