This document outlines the top 5 Magento secure coding best practices: 1) Validate all input as strictly as possible using validation libraries, 2) Use parameterized queries to prevent SQL injection, 3) Escape all user input to prevent XSS attacks, 4) Use CSRF tokens on forms to prevent CSRF attacks, and 5) Implement security headers to enable browser protections. It provides code examples for each practice and additional resources for learning about application security best practices.