The following are several of the resources covered in the [Art of Hacking Series LiveLessons](https://theartofhacking.org), [Safari Live Training](https://www.safaribooksonline.com/search/?query=ethical%20hacking%20omar%20santos&extended_publisher_data=true&highlight=true&is_academic_institution_account=false&source=user&include_assessments=false&include_case_studies=true&include_courses=true&include_orioles=true&include_playlists=true&formats=live%20online%20training&sort=relevance), and [penetration testing books authored by Omar Santos](https://omarsantos.io).
Dex2jar and JD-GUI are two different tools that are often used for reverse engineering Android apps. Dex2jar converts .dex files to .jar. JD-GUI is a Java decompiler that can decompile .jar files to the original Java source.