What is the most effective method to prevent an industrial control system from being exploited by external attackers?

Air gapping is regarded as the most effective method to prevent an industrial control system from being exploited by external attackers because it involves physically isolating the control system from any external networks, including the internet. This means that there are no direct network connectivity pathways for external attackers to exploit, significantly reducing the risk of unauthorized access and cyberattacks.

By keeping the industrial control system physically separated from other networks, the risks associated with malware infections, remote hacking attempts, and data breaches are also mitigated. Without the possibility of incoming or outgoing data over network connections, the attack surface for potential threats is greatly minimized.

While firewalling, encryption, and IP filtering can provide additional layers of security, they do not offer the same level of protection as air gapping. Firewalls can be misconfigured or inadequately maintained, encryption may protect data in transit but does not prevent attacks on systems directly, and IP filtering can be bypassed with spoofing techniques. Therefore, air gapping remains the most robust defense against external threats targeting industrial control systems.