This can help with brute force attacks.
The delay engine creates the appearance of a delay when checking user and pass credentials. This delay makes it harder for brute force attacks to determine if a username is valid versus one that is not.
more here: http://www.proftpd.org/docs/modules/mod_delay.html
kindly guide me how can I create password protected FTP? I tried several ways but without password my FTP is working just perfect, and whenever I tried to use it with user and password it isn't working. Please help.