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Step 4: Set up a firewall

Using a properly configured firewall is a required step in ensuring computer security.

What is a firewall?

When properly configured, a computer firewall protects your computer from intruders who exploit flaws in your computer's software to create annoyances or to steal or damage your data.

A firewall is not the same as anti-virus software or anti-spyware software -- it's best if you have all of these since each protects your computer in a different way.

Why do I need a firewall?

If your computer doesn't have a properly configured firewall, it could:

  • spread viruses to people listed in your address book
  • allow intruders to record your keystrokes or view or delete your data
  • allow intruders to send spam from your computer
  • execute distributed denial of service attacks on other computers

-- all without your knowledge.

Intruders can gain access to your computer through your computer's open network ports, which are communications channels for programs. A firewall can secure any ports which might be open on your computer.

More information: How Firewalls Work and Frequently Asked Questions About Internet Firewalls.

To determine how to set up a software firewall, what operating system does your computer have?

Not Sure

  • Windows 7 or Vista: Select Start. Type winver and press Enter.
  • Windows XP: Select Start > Run. Type winver and press Enter.
  • Mac: Select "About this Mac" from the Apple menu.

Windows 7,
Windows Vista,
Windows XP

Ensure that Windows Firewall or any other firewall is working properly by opening Security Center in Start > Control Panel > Security.

Mac OS 10.5 and 10.6

  1. Open System Preferences, then open Security.
  2. Select the Firewall tab, then select either one of the following:
    1. Allow only essential services.
    2. Set access for specific services and applications.

Mac OS 10.3 or 10.4

  1. Open System Preferences, then open Sharing.
  2. Select the Firewall tab, then select the Start button.

Test your firewall

  1. Test that the firewall protects your computer by visiting one or more of the following test sites:
    1. ShieldsUp!
    2. Sygate Online Services
    3. the Security Scan feature of Symantec Security Check
    4. LeakTest
  2. If your firewall is protecting your computer, congratulations! Proceed to Step 5: Install operating system updates.

Help? Feedback?

Try asking your question in the Craigslist computer forum. To provide feedback for this page, send the URL and your comments to Web & Data Services Manager Frank Farm at farmf@pharmacy.ucsf.edu.

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