Install only what is required.
Lock and expire default user accounts.
Enforce password management.
Enable data dictionary protection.
Practice the principle of least privilege.
Grant necessary privileges only.
Revoke unnecessary privileges from the PUBLIC user group.
Restrict permissions on run-time facilities.
Enforce access controls effectively and authenticate clients stringently.
Use a firewall.
Never poke a hole through a firewall.
Protect the Oracle listener.
Monitor listener activity.
Monitor who accesses your systems.
Check network IP addresses.
Encrypt network traffic.
Harden the operating system.
Apply all security patches and workarounds.
Contact Oracle Security Products if you come across vulnerability.