Again something very interesting in Humble Bundle! This time it's Cybersecurity books bundle presented by Wiley. These ebooks are all available in PDF format, and some in ePUB and MOBI too. It all can be found on this website.

At least $1:

Social Engineering: The Art of Human Hacking

The Web Application Hacker's Handbook: Finding and Exploiting Security Flaws, 2nd Edition

Practical Reverse Engineering: x86, x64, ARM, Windows Kernel, Reversing Tools, and Obfuscation

Threat Modeling: Designing for Security

At least $8:

All above and:

Security Engineering: A Guide to Building Dependable Distributed Systems, 2nd Edition

The Shellcoder's Handbook: Discovering and Exploiting Security Holes, 2nd Edition

Cryptography Engineering: Design Principles and Practical Applications

The Art of Deception: Controlling the Human Element of Security

The Art of Memory Forensics: Detecting Malware and Threats in Windows, Linux, and Mac Memory

At least $15:

All above and:

Malware Analyst's Cookbook and DVD: Tools and Techniques for Fighting Malicious Code

Unauthorised Access: Physical Penetration Testing For IT Security Teams

Secrets and Lies: Digital Security in a Networked World, 15th Anniversary Edition

CEH v9: Certified Ethical Hacker Version 9 Study Guide

Applied Cryptography: Protocols, Algorithms and Source Code in C, 20th Anniversary Edition