Securing Enclave Interiors 183 Table 7.5 Varying Levels of Host Security Options Device HMI or similar device running a modern operating system. Application is not time sensitive HMI or similar device running a modern operating system. Application is time sensitive PLC, RTU, or similar device running an embedded commercial OS PLC, RTU, IED, or similar device running an embedded operating environment Suitable Security Measures l l l l Host firewall HIDS Anti-Virus or Application Whitelist Disable all unused ports and services Host firewall Disable all unused ports and services Host firewall or HIDS if available External security controls External security controls l l l l l Selecting Interior Security Systems As a matter of best practices, all host access controls and host network security solutions should be implemented on all networked devices. However, not all net-