There are so many hackers or what ever name for them, want to login ftp server of my VPS server.
The one of the most simplest way is to deny all IP address except specific IP address.
The FTP server running on VPS is Proftpd.
To do the limitation, just edit /etc/proftpd.conf
Add the following in the end.
Order allow,deny Allow from 96.49., 64.180., 24.81. Deny from all