The convergence of Operational Technology and Information Technology is driving integration of the Internet of Things and Industrial Control Systems to form the Industrial Internet of Things. Due to the influence of Information Technology, security has become a high priority particularly when implementations expand into critical infrastructure. At present there appears to be minimal research addressing security considerations for industrial systems which implement application layer IoT messaging protocols such as Data Distribution Services (DDS). Simulated IoT devices in a virtual environment using the DDSI-RTPS protocol were used to demonstrate that enumeration of devices is possible by a non-authenticated client in both active and passive mode. Further, modified sequence numbers were found to be a potential denial of service attack, and malicious heartbeat messages were fashioned to be effective at denying receipt of legitimate messages.