My plugin searched for malicious code in ASCII files like PHP and JS files. The default settings skip all the typical Binary file types like images and PDF files that are common on webservers because they are usually much larger than text files and do not contain executable code. Even if a hacker were to place malicious code into a Binary file type it could not be executed on your webserver without being included in another PHP file, and that is already something my plugin is looking for.
You can change the list of file type to skip, but it will only make it take much longer to scan all your files.
Please let me know if you have any other questions or concerns.
Aloha, Eli