1. SSH to the server that has VsFTP, and SU to it.
2. Edit file /etc/vsftpd/vsftpd.conf, find line
anonymous_enable=YES
change to
anonymous_enable=NO
3. Do /sbin/service vsftpd restart
4. Try to ftp to domain or IP without providing a user/password. Access will be rejected.

Anonymous FTP has been rejected!