The Prevent Direct Access – Protect WordPress Files plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 2.8.8 via the 'generate_unique_string' due to insufficient randomness of the generated file name. This makes it possible for unauthenticated attackers to extract sensitive data including files protected by the plugin if the attacker can determine the file name.
https://plugins.trac.wordpress.org/browser/prevent-direct-access/trunk/includes/helper.php#L16
https://plugins.svn.wordpress.org/prevent-direct-access/tags/2.8.8/includes/helper.php