What type of firewall is typically used in a public setting where network systems are untrusted?

The type of firewall typically used in a public setting where network systems are untrusted is a public firewall. Public firewalls are designed to protect devices connected to a public network, such as those found in cafes, airports, or other public access points. These firewalls help to safeguard a user's data from potentially malicious actors on the same network.

Public firewalls typically enforce strict security rules, controlling incoming and outgoing traffic. They are essential in scenarios where users are accessing the internet through unsecured networks, as they can prevent unauthorized access to devices and sensitive information.

In contrast, the other options refer to use cases that may not specifically focus on public trust issues. An external firewall might protect an entire network from external threats but does not specifically imply a public or untrusted setting. Work and home firewalls are typically configured for trusted environments where users are known, thus they do not provide the same level of protection in public access situations where untrusted devices are common.