-//This is the list of blocked extensions, you can remove extensions or add to this list as you like
-define ("CONFIG_BLOCKED_EXTENSIONS", serialize(array("exe", "scr", "rar", "zip", "com", "vbs", "bat", "cmd", "html", "htm", "msi", "php", "php5")));
+//Operate on a BLACKLIST or a WHITELIST when blocking file extensions
+define("CONFIG_EXTENSION_BLOCKING_MODE", "BLACKLIST");
+//This is the list of blocked extensions in BLACKLIST mode (default mode), you can remove extensions or add to this list as you like
+define("CONFIG_BLOCKED_EXTENSIONS", serialize(array("exe", "scr", "rar", "zip", "com", "vbs", "bat", "cmd", "html", "htm", "msi", "php", "php5")));
+//This is the list of allowed extensions in WHITELIST mode, you can remove extensions or add to this list as you like
+define("CONFIG_ALLOWED_EXTENSIONS", serialize(array("txt", "pdf")));