A "phishing kit" is small piece of software usually written in PHP, HTML, and JavaScript that mimics legitimate portals (for example, financial institution websites) in order to acquire sensitive information such as usernames, passwords, and credit card details. The phishing kits of the first generation were quite simple; the fraudster would build a login page to collect stolen information on local files, saved on the compromised web servers. As shown in the picture below, after the credentials have been saved, users are redirected to the legitimate website.

This approach has an obvious drawback: if the directory-listing feature is enabled on the web server, other Internet users (including the compromised financial institutions) would be able to read those files. The countermeasure that was adopted by the fraudsters was...