Linux is by design very secure and stable. However, you need to take some precautions and steps in order to keep it so. Here are a few basic steps to maintaining a secure Linux system:
Never use the root account for normal use: After Linux is installed, it will create two accounts—root and normal user. The root account allows unlimited access to system files and folders. So, for normal use do not use the root account. If you mess up with the system files, it can crash your Linux installation.
Limit network services: Enable only the services you need. If you don’t need a mail server, don’t install it. And if you are not going to service web pages, don’t install a web server. Hackers usually compromise computers and networks using bad configured network services. The best way to get protection from them is to turn off all network services which are unnecessary.
Use trusted software sources: Always use trusted software sources. Software from unknown repositories may contain bugs and vulnerabilities which can crash your system. For this reason, always install software from official repositories. Depending on your Linux distribution, you should be able to find any software you need in the repositories. If you have to install software from elsewhere, read reviews before installing it.
Use strong passwords: Always use strong passwords. “123456″ or “asdfgh” don’t cut the slack anymore. Use smaller, upper case letters and numbers in your passwords and make them long. Never use passwords that can be guessed easily. Do not use the same password on multiple systems or email or other accounts. And don’t write your complete password anywhere.
Always use common sense—this is the root to security. If an email turns up in your inbox saying you need to update your password or something similar, think twice before acting.