This paper is about discovering vulnerabilities inside the files that make up WordPress themes. It also discusses reverse engineering of encoded PHP files, common tools, exploits, and dangerous copyright protection mechanisms.
You can download it from the following link: https://packetstormsecurity.com/files/download/111237/wordpress-themes.pdf
Source: https://packetstormsecurity.com/files/111237/Analyzing-WordPress-Themes.html