Here are some quick tips on how to secure your Linux server. This is only a short list, but, they are must do’s! Some of which are:
1. Change ssh port (use keys if possible as well/allow only specific users)
2. Disable unneeded services
3. Install a good firewall
4. Disable dangerous / unused PHP functions / harden your PHP
5. Install mod_security
6. Virus scan FTP uploads
7. Install root kit detection
8. Set root email to off server email account
9. Make sure your passwords are tough to guess. This is a big one, especially for the root user, this should be a very tough password.
This is a quick list, as there are many other things that can be done. Some things on this list are already on this blog, so please be sure to read the related posts.