● Physically protect all equipment, i.e., ensure that physical access to computers, network
equipment and cables, controllers, I/O systems, power supplies, etc., is limited to authorized
persons
● When connecting a trusted network zone to outer networks, make sure that all connections
are through properly configured secure interconnections only, such as a firewall or a system
of firewalls, which is configured for “deny by default”, i.e., blocks everything except traffic
that is explicitly needed to fulfill operational requirements.
● Allow only authorized users to log on to the system, and enforce strong passwords that are
changed regularly.
● Continuously maintain the definitions of authorized users, user groups, and access rights,
to properly reflect the current authorities and responsibilities of all individuals at all times.
Users should not have more privileges than they need to do their job.
● Do not use the system for e-mail, instant messaging, or internet browsing. Use separate
computers and networks for these functions if they are needed.
● Do not allow installation of any unauthorized software in the system.
● Restrict temporary connection of portable computers, USB memory sticks and other remov-
able data carriers. Computers that can be physically accessed by regular users should have
ports for removable data carriers disabled.
● If portable computers need to be connected, e.g., for service or maintenance purposes, they
should be carefully scanned for viruses immediately before connection.
● All CDs, DVDs, USB memory sticks and other removable data carriers, and files with
software or software updates, should also be checked for viruses before being introduced
into the trusted zone.
● Continuously monitor the system for intrusion attempts.
● Define and maintain plans for incident response, including how to recover from potential
disasters.
● Regularly review the organization as well as technical systems and installations with respect
to compliance with security policies, procedures and practices.
A protected local control cabinet could look like in figure 23, page 77. This network is not
connected to any external network. Security is primarily a matter of physically protecting the
automation system and preventing unauthorized users from accessing the system and from
connecting or installing unauthorized hardware and software.
Fig. 23: Isolated automation system
Servers and workplaces that are not directly involved in the control and monitoring of the
process should preferably be connected to a subnet that is separated from the automation
system network by means of a router/firewall. This makes it possible to better control the
network load and to limit access to certain servers on the automation system network. Note that
servers and workplaces on this subnet are part of the trusted zone and thus need to be subject
to the same security precautions as the nodes on the automation system network.
Configuration and programming
Cyber security > Secure operation
2023/03/03
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