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What are Windows Firewall and Windows Defender?

3 of 10 in Series: The Essentials of Home Network Security

Windows Firewall and Windows Defender are programs included with Windows 7 that help protect your home network and keep your data secure from Internet threats. Today's Internet threats are prolific, and new computer security risks are discovered and exploited literally every day.

As high-speed Internet access has become less expensive, always-on DSL or cable modem connections for home users have eclipsed old-fashioned dialup Internet connections in popularity — thus the need for firewalls to protect home networks as well. In addition to antivirus protection and firewalls, antispyware software is a necessary element in your security arsenal.

Windows Firewall

A firewall, at its most basic level, permits or denies communications between computers, between networks, or between computers and networks (for example, your home computer and the Internet) based on the firewall’s configuration rules. You can access the settings for Windows Firewall through the Network and Security section in the Control Panel.

Almost all computers and networks communicate by establishing connections between two hosts using an IP address and a port. Although there are many types of firewalls, the most common type of firewall (and the type used in Windows 7, provided by Windows Firewall) permits or denies communications based on IP address and port information.

Only connections that are explicitly allowed, using firewall rules, are permitted. Windows Firewall, by default, allows all outbound connections, and permits only established inbound connections (that is, an inbound connection that is in direct response to an outbound connection initiated from your computer or network).

There are firewalls protecting Microsoft’s Web servers and your ISP’s DNS servers. In order for your computer to connect to Microsoft’s Web servers, Microsoft must first create firewall rules to allow the communication. This is accomplished by creating a firewall rule that essentially says to allow any inbound IP address to connect to 207.46.232.182 (Microsoft’s Web server) on port 80 (HTTP). Your ISP must create a similar rule on their firewall that essentially says to allow any inbound IP address to connect to its DNS servers on port 53 — which is the standard port for DNS.

Windows Firewall permits your outbound DNS request to your ISP’s DNS server, and your computer’s outbound HTTP request to Microsoft’s Web server. In your outbound request, your computer first sends the DNS request to your ISP’s DNS server on port 53, and tells your ISP’s DNS server on what port it will be listening for a response.

Your computer selects a random port number between 49,152 and 65,535, and Windows Firewall automatically creates a temporary rule that allows an inbound connection from the IP address of your ISP’s DNS server to the IP address of your computer, on that random port number.

After the response is received (or if a response is not received within a specified period of time, say 30 seconds), the rule is automatically deleted from the firewall and the connection is again blocked. A similar process is then repeated to connect to Microsoft’s Web server.

Windows Defender

Windows Defender is Microsoft’s free antispyware program that is included in Windows 7. Like Windows Firewall, Windows Defender is enabled by default, and no configuration is required for it to begin protecting your computer.

There are some Windows Defender settings you may want to customize, such as how often and when your computer is automatically scanned, what Windows Defender does when spyware is detected, and what you want scanned or excluded (such as certain programs, files, folders, or e-mail). You can access these settings through the Network and Security section in the Control Panel.

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