One popular usage of SSH is to allow users to access a command shell on a remote computer for administrative purposes, normally TCP port 22 is used by it. SSH logins are very sensitive to brute force attacks. A thousand things can go wrong which could give someone unauthorized access to your server. As long as people use weak passwords, the bad guys will be trying to brute force them.
Because a lot of people with SSH servers use weak passwords, many online attackers will look for an SSH server, then start guessing passwords at random. An attacker can try thousands of passwords in an hour, and guess even the strongest password given enough time. The recommended solution is to use SSH keys instead of passwords.
The best way to secure your SSH login is to use Public/Private PEM keys. This is default login type for Amazon EC2 servers. In this post will show you how to use PEM file to login to your VPS or any other Ubuntu server.