Quantum Computation and Quantum Information by Nielsen and Chuang
if you're interested in theoretical computer science, the frontier is quantum computing. Quantum Computation and Quantum Information by Nielsen and Chuang (http://squint.org/qci/) is basically the closest thing to a treatise on the subject available today. this book covers the fundamentals of all areas of quantum computing, and it is a much easier read than more mathematical texts such as Kitaev, Shen and Vyalyi.
specifically in regards to computer security, quantum computing has been driven solely by the discovery of a fast quantum algorithm for factoring numbers by Shor. the first person to invent a serious quantum computer with reliable error correction and several qubits can theoretically break RSA, rendering modern cryptosystems obsolete.
the subject itself is sometimes difficult to grasp but not impossible. thinking in the quantum realm requires some serious abstract thought. i encourage you to check it out. does anybody have any thoughts on the matter?