The short answer
A firewall is a security system that monitors and controls network traffic between your device and the internet, blocking unauthorized access based on predetermined rules while allowing legitimate communication to pass through freely.
What a Firewall Does
A firewall acts as a barrier between your computer or network and the internet. It examines every piece of data attempting to enter or leave your system and decides whether to allow or block it based on security rules. Think of it as a security guard checking credentials at a building entrance—it inspects incoming and outgoing traffic and stops anything that looks suspicious or doesn't meet the required criteria.
Firewall versus Antivirus
Firewalls and antivirus software protect your system in fundamentally different ways:
- A firewall controls network traffic and prevents unauthorized access to your device. It stops threats at the network level before they reach your system.
- Antivirus software scans files, programs and emails already on your computer to detect and remove malicious code like viruses, trojans and spyware.
- Firewalls are preventive barriers; antivirus tools are detection and removal systems.
- You need both for comprehensive protection—the firewall keeps many threats out, while antivirus catches malware that slips through or arrives via physical media.
Hardware versus Software Firewalls
Hardware firewalls are physical devices that sit between your network and the internet connection. Your home router typically includes a basic hardware firewall. These protect every device connected to the network simultaneously and operate independently of any computer's operating system. They cannot be disabled by malware on an individual computer.
Software firewalls run as programs on individual devices. Windows Firewall, macOS Firewall and third-party options like ZoneAlarm are software firewalls. They offer more granular control over specific applications and can create different rules for different programs on that specific device. However, they consume system resources and can potentially be disabled by malware.
For home users, the combination of your router's hardware firewall and your operating system's software firewall provides layered security—each adds protection the other cannot provide alone.
Risks of Disabling Your Operating System Firewall
Turning off your built-in firewall exposes your device to significant threats:
- Unauthorized access: Attackers can potentially connect directly to your computer and access files, install malware or monitor your activity.
- Worm infections: Network worms can spread automatically to unprotected devices without any action on your part.
- Data theft: Open ports allow malicious programs to send your personal information to remote servers.
- Your device becoming part of a botnet: Compromised computers are often used to attack other systems or send spam.
Some legitimate software installations request that you temporarily disable your firewall, but you should re-enable it immediately afterward. If specific programs need network access, create firewall exceptions for those applications rather than disabling protection entirely. The performance impact of modern firewalls is negligible compared to the security risk of operating without one.