Managing your linux machine from remote is a great thing, but you shouldn't allow root to logging in from SSH. Or at least when it's reachable from outside. There are anonymous groups active who will beat you up when when you allow this. Naah just a joke, I will beat you up personally. Or you could read this article.
Everyone knows that every Linux operating system has a user called 'root' who can do anything in the system. Root is the root. It can even take your dog away for a walk!
Because everyone knows that this user exists, they only need to guess the password to break in to your system by doing a brute force attack. So someone starts some script or bot who will do continuously login attempts with generated passwords. So the first thing you need to do is disallowing root access. Or even better, have a white list with IP addresses where you will allow SSH connections from. Or if this is not an option, just block IP addresses where many unsuccessful login attems are made.I will write an article about that too but in the meanwhile take a look at DenyHosts.
Open the sshd_config file:
sudo vim /etc/ssh/sshd_config
Look for this line:
After a clean install you would see that this line is usually commented. This means it will use the default value with is be YES. So having this line commented means that you will allow root login. Holy shit bro, look out I might stand behind you with a baseball bat!
Just change this line into:
Restart sshd to apply the changes:
sudo /etc/init.d/sshd restart
So how are you supposed to login now? You need to have a normal user with administrator rights or adding the user into sudoers by using visudo. Don't edit the /etc/sudoers file directly. Just do it with visudo because it will validate the changes you have done. if you screw this up, then sudo is not working properly.