Securing SSH is vitally important. Here are a few simple steps which will help you secure SSH on your server.
The first thing you should do is change the port that SSH listens on. This will help prevent automated-hacking tools from trying to brute force their way into your server.
To do this, open your SSH client (Putty is recommended).
Login to your server.
At the command line, you need to go to /etc/ssh
To do this, type "cd /etc/ssh" and hit enter.
You then need to edit the SSH config file. To do this, type "vi sshd_config" at the command prompt.
You will then be presented with the SSH config, please be careful when editing this file - as if you break it, SSH can fail and you will not be able to access your server.
You need to look for the line which should look like the following:
To change the SSH port, simply hit the insert key on your keyboard, and change 22 to a port of your choice. Please make sure that you open the port in any firewall modules which you have installed, and that the port isn't already in use by some other application.
When you have changed the port number, simple hit escape on your keyboard, and then type ":wq" and hit enter. This will save the file and return you to the console.
When this is done, you'll need to restart SSH as follows:
"service sshd restart"
When I get a bit more time, I'll explain on how to disable Password Authentication, to make your server more secure.