In which platform your are running this ?
- Install Firewall (APF or CSF Firewall with BFD)
- ModSecurity (Web application firewall)
- ModEvasive (Prevent DDOS attacks)
- Harden SSH server
- Fix Open DNS Recursion
- Install RKhunter
- Install ClamAV (Antivirus)
- XInet Servers Hardening (Disable Telnet/Finger or unwanted services)
- Securing PHP
- PortsEntry (tool to detect portscans)
- Harden host.conf (against IP spoofing)
- Check User Uploaded files
- Secure /tmp Folders (noexec, nosuid)
If you have done above stuffs in a Linux server then you are almost there, but always the application vulnerabilities results in hack, so make sure that you update the software regular.