In computer networks and security, a firewall is primarily used to protect a system or network against which type of threat?

Introduction / Context:
Firewalls are a fundamental part of network security architecture. They act as gatekeepers between trusted internal networks and untrusted external networks such as the internet. This question checks whether you know the primary purpose of a firewall and can distinguish it from the roles of antivirus software, physical safety systems and other protective tools. Correctly identifying what a firewall does is essential for basic computer security awareness.

Given Data / Assumptions:

• The focus is on firewalls in the context of computer and network security.
• The question asks what firewalls protect against.
• Options mention virus attacks, unauthorized access, physical fire, power problems and paper jams.
• We assume a standard firewall that filters network traffic based on rules and policies.

Concept / Approach:
A firewall monitors and controls incoming and outgoing network traffic based on predefined security rules. Its main purpose is to prevent unauthorized access to or from a private network. It can block suspicious traffic, restrict ports and protocols and enforce access control policies at the network perimeter or on individual hosts. Although some firewalls can help reduce exposure to certain malware by blocking malicious traffic, dedicated antivirus software is the main tool for scanning and removing viruses from files. Firewalls do not protect against physical fire, power failures or mechanical issues like paper jams. Therefore, the correct answer is that firewalls are used to protect against unauthorized access from untrusted networks.

Step-by-Step Solution:

Verification / Alternative check:
Network security guides and certification material describe firewalls as access control devices that enforce security policies on network boundaries. Definitions emphasise filtering packets, blocking unwanted connections and establishing demilitarised zones to protect internal systems from external attackers. While some next generation firewalls integrate additional features like intrusion prevention, their core role remains controlling who and what can access systems across the network. None of these references describe firewalls as devices that directly extinguish physical fires or fix paper jams. This confirms that unauthorized access is the correct focus of firewall protection in exam style questions.

Why Other Options Are Wrong:

• Virus attacks inside individual files only: Firewalls may block some malicious traffic, but antivirus software is the main defence against viruses within files.
• Physical fire and heat damage to hardware: Handled by fire alarms and extinguishers, not by network firewalls.
• Power failure and electrical surges: Managed by UPS systems and surge protectors, not by software or hardware firewalls.
• Printer paper jams in an office: A mechanical issue completely unrelated to network traffic or firewalls.

Common Pitfalls:
Because the word firewall sounds similar to physical fire protection, some learners mistakenly assume that it has something to do with preventing real fire. Others think that any security problem, including viruses, is handled by the firewall. To avoid these errors, remember that a firewall deals with network traffic, not with files already on a computer or with the physical environment. When exam options mix several types of threats, choose the one that best matches network access control, which is unauthorized access from untrusted networks.

Final Answer:
Firewalls are primarily used to protect systems and networks against Unauthorized access from untrusted networks.