Hot answers tagged security-theater
You can't secure FTP. Remove it and replace with a secure alternative like SFTP if you need file transfer. The way in which you've asked the question implies that you don't have a valid need for it, that it's probably just on by default. Depending on what you're running, 'rpm -e pure-ftpd' or 'dpkg -r pure-ftpd' might do for you.
FTP is a very old protocol and not recommended anymore today because credentials are transmitted in plaintext which can be read by sniffing the network traffic. If you don't need it you should uninstall it or you can block this port with a firewall. On Linux you could use iptables to block all traffic to this port as follows: iptables -A INPUT -p tcp ...
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