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What is a firewall?

On a computer or network, a firewall blocks unwanted connections, usually from the internet. This is different from a fire wall in a house or a car. A firewall is not antivirus. The NCSC describes it as a tool that blocks unwanted connections, usually from the internet, from reaching a device. 12

By Secordit. Last checked: 10 November 2026.

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How it works

  1. The firewall checks network connections and can block unwanted ones before they reach the device or network. 1
  2. Modern devices often have a firewall, and antivirus, built in and turned on, but you should still check that they are on. 1
  3. Firewalls are one of the five Cyber Essentials technical controls. That is a description of the scheme, not a claim about any certificate. 23

How it can look

The NCSC small-organisations guide says you should check that the built-in firewall and antivirus on modern devices are on. It points to vendor instructions for Windows and Apple computers. Checking that setting is a practical step for a household or a small team. 1

Warning signs

  • The built-in firewall on a computer or router has been switched off, or was never turned on. 1
  • A seller treats a firewall as if it were antivirus, or as if it were the only control needed. 12
  • A new device has been set up, and the built-in firewall has not been checked. 1

What to do now

  1. Check that the built-in firewall on your computer, and on your router if you can, is switched on. Use the vendor instructions for Windows or Apple if you need them. 1
  2. Keep the built-in antivirus switched on as well, because a firewall is not antivirus. 1
  3. Treat the firewall as one layer, alongside software updates and careful use of email and websites. 12

UK reporting and support

  • If you think a device is infected, follow the NCSC help for infected devices. 4
  • For fraud or hacking in England, Wales or Northern Ireland, use Report Fraud. In Scotland, call Police Scotland on 101. 578
  • If money has gone or banking details were shared, call your bank using the number on your card. Or use 159 if your bank participates. 6
  • If someone is in danger, call 999. 78

How to protect yourself

  • Leave the built-in firewall on, and check it after a new device is set up. 1
  • Apply software updates, which can include fixes for the system that runs the firewall. 12
  • Do not expect a firewall to replace careful checks on messages, links and sign-in details. 1

Frequently asked questions

Is the firewall on my Windows laptop enough, or do I need to buy another one?

The NCSC small-organisations guide says modern devices often have a firewall and antivirus built in, and that you should check they are on. It does not say you must buy a separate firewall product for a typical laptop. 1

Is a firewall the same as antivirus?

No. A firewall blocks unwanted network connections. Antivirus looks for harmful software. You need to check that both built-in tools are on. 1

Does a firewall stop phishing?

A firewall blocks unwanted connections, usually from the internet. It is not antivirus. Phishing often arrives as a message, so checking unexpected messages and links still matters. 12

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General information, not legal, financial or personalised security advice. Secordit is not a police or bank reporting service.

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Sources

  1. NCSC, Protecting your devices | National Cyber Security Centre. Accessed 10 November 2026 (Europe/London).
  2. NCSC, Cyber Essentials overview | National Cyber Security Centre. Accessed 10 November 2026 (Europe/London).
  3. NCSC, Cyber Essentials resources | National Cyber Security Centre. Accessed 10 November 2026 (Europe/London).
  4. NCSC, Help for individuals | National Cyber Security Centre. Accessed 10 November 2026 (Europe/London).
  5. Report Fraud, Report Fraud. Accessed 10 November 2026 (Europe/London).
  6. Stop Scams UK, 159 Phone number - Stop Scams UK. Accessed 10 November 2026 (Europe/London).
  7. Police Scotland, How to report a crime - Police Scotland. Accessed 10 November 2026 (Europe/London).
  8. Report Fraud, Reporting cyber crime and fraud or phishing attempts - Report Fraud. Accessed 10 November 2026 (Europe/London).