Which of the following would be MOST appropriate to secure an existing SCADA system by
preventing connections from unauthorized networks?

A.
Implement a HIDS to protect the SCADA system

B.
Implement a Layer 2 switch to access the SCADA system

C.
Implement a firewall to protect the SCADA system

D.
Implement a NIDS to protect the SCADA system

Explanation:
Firewalls manage traffic using filters, which is just a rule or set of rules. A recommended guideline
for firewall rules is, “deny by default; allow by exception”. This means that if a network connection
is not specifically allowed, it will be denied.