Отключайте ssh авторизацию по паролю

Всегда, абсолютно всегда отключайте ssh авторизацию по паролю. Даже если Вы используете сильный пароль.

Просто взгляните на логи:

May  9 04:10:17 localhost sshd[20429]: Failed password for root from 221.194.47.233 port 50650 ssh2
May  9 04:10:18 localhost sshd[20431]: Failed password for root from 116.31.116.36 port 34071 ssh2
May  9 04:10:19 localhost sshd[20429]: Failed password for root from 221.194.47.233 port 50650 ssh2
May  9 04:10:20 localhost sshd[20431]: Failed password for root from 116.31.116.36 port 34071 ssh2
May  9 04:10:22 localhost sshd[20429]: Failed password for root from 221.194.47.233 port 50650 ssh2
May  9 04:10:22 localhost sshd[20429]: Received disconnect from 221.194.47.233 port 50650:11:  [preauth]
May  9 04:10:22 localhost sshd[20429]: Disconnected from 221.194.47.233 port 50650 [preauth]
May  9 04:10:22 localhost sshd[20429]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=221.194.47.233  user=root
May  9 04:10:22 localhost sshd[20431]: Failed password for root from 116.31.116.36 port 34071 ssh2
May  9 04:10:23 localhost sshd[20431]: Received disconnect from 116.31.116.36 port 34071:11:  [preauth]
May  9 04:10:23 localhost sshd[20431]: Disconnected from 116.31.116.36 port 34071 [preauth]
May  9 04:10:23 localhost sshd[20431]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=116.31.116.36  user=root
May  9 04:10:25 localhost sshd[20433]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=221.194.47.233  user=root
May  9 04:10:26 localhost sshd[20433]: Failed password for root from 221.194.47.233 port 32882 ssh2
May  9 04:10:32 localhost sshd[20433]: message repeated 2 times: [ Failed password for root from 221.194.47.233 port 32882 ssh2]
May  9 04:10:32 localhost sshd[20433]: Received disconnect from 221.194.47.233 port 32882:11:  [preauth]
May  9 04:10:32 localhost sshd[20433]: Disconnected from 221.194.47.233 port 32882 [preauth]
May  9 04:10:32 localhost sshd[20433]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=221.194.47.233  user=root
May  9 04:10:35 localhost sshd[20435]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=58.218.198.160  user=root
May  9 04:10:35 localhost sshd[20437]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=221.194.47.233  user=root
May  9 04:10:37 localhost sshd[20435]: Failed password for root from 58.218.198.160 port 60580 ssh2
May  9 04:10:37 localhost sshd[20437]: Failed password for root from 221.194.47.233 port 45652 ssh2
May  9 04:10:39 localhost sshd[20435]: Failed password for root from 58.218.198.160 port 60580 ssh2
May  9 04:10:40 localhost sshd[20437]: Failed password for root from 221.194.47.233 port 45652 ssh2
May  9 04:10:42 localhost sshd[20435]: Failed password for root from 58.218.198.160 port 60580 ssh2

К абсолютно новому серверу, сразу же начинают подбирать пароль с множества ботов. Со скоростью от 50 до 200 запросов в минуту.

Так же желательно полностью отключить авторизацию под рутом и классическими логинами adm/admin/administrator. Эта рекомендация уже распространяется не только на ssh, а на любые сервисы: веб-сайты, фтп, ssh, бд итд.