Windows 7 : Blocking Hackers with Windows Firewall (part 1)

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1. How Firewalls Work

To understand what a firewall is, you need to first understand what a network connection is. Even though you have only one skinny set of wires connecting your computer to the Internet (through a phone line or cable outlet), that connection actually consists of 65,535 ports. Each port can simultaneously carry on its own conversation with the outside world. So, theoretically, you could have 65,535 things going on at a time. Of course, nobody ever has that much going on all at one time. A handful of ports is more like it.

The ports are divided into two categories: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP is generally used to send text and pictures (Web pages and e-mail), and includes some error checking to make sure all the information that's received by a computer matches what the sending computer sent. UDP works more like broadcast TV or radio, where the information is just sent out and there is no error checking. UDP is generally used for real-time communications, such as voice conversations and radio broadcasts sent over the Internet.

Each port has two directions: incoming (or ingress) and outgoing (or egress). The direction is in relation to stuff coming into your computer from the outside: namely the Internet. It's the stuff coming into your computer that you have to watch out for. But you can't close all ports to all incoming traffic. If you did, there'd be no way to get the good stuff in. But you don't want to let everything in, either. You need a way to separate the wheat from the chaff, so to speak — a way to let in the good stuff while keeping out the bad stuff.

Antispyware and antivirus software are good tools for keeping out viruses and other bad things that are attached to files coming into your computer. But hackers can actually sneak worms and other bad things in through unprotected ports without involving a file in the process. That's where the firewall comes into play. A stateful firewall, such as the one that comes with Windows 7, keeps track of everything you request. When traffic from the Internet wants to come in through a port, the firewall checks to make sure the traffic is something you requested. If it isn't, the firewall assumes this is a hacker trying to sneak something in without your knowing it, and therefore prevents the traffic from entering your computer. Figure 1 illustrates how it works.

Figure 1. How a stateful firewall works.

So, there's really more to it than just having a port open or closed. It's also about filtering. About making sure that data coming into an open port is something you requested and not some rogue uninvited traffic sent by some hacker. Many of the worms that infected so many computers in the 1990s did so by sneaking in undetected through unfiltered ports. These days, you really want to make sure you have a firewall up whenever you go online to prevent such things.

1.1. What a Firewall Doesn't Protect Against

It's important to understand that a firewall alone is not sufficient protection against all Internet threats. A firewall is just one component in a larger defense system. Specifically:

  • Windows firewall doesn't protect you from spyware and viruses.

  • Windows firewall doesn't protect you from attacks based on exploits. 

  • A firewall doesn't protect you from pop-up ads.

  • A firewall doesn't protect you from phishing scams.

  • Windows firewall doesn't protect you from spam (junk e-mail).

So, a firewall isn't a complete solution. Rather, it's an important component of a larger security strategy.


Note that in the preceding list, I indicated that Windows Firewall doesn't provide certain types of protection, such as spam or virus blocking. Many hardware firewalls do provide this type of protection. This is sometimes call perimeter protection, because it protects your network from threats at the perimeter of your network. These types of firewalls can cost from several hundred to several thousands of dollars, so they aren't always the best bet for a home network. They can be extremely valuable, however, for business networks.

2. Introducing Action Center

Before you get into Windows Firewall, take a look at the Action Center. This is a single point of notification for most of your PC's security. You can open the Action Center in several ways. Use whichever is most convenient for you:

  • Right-click the flag icon in the Notification area and choose Action Center.

  • Press , type act, and click Action Center.

  • Click the Start button, choose Control Panel, click System and Security, and then click Action Center.

Whichever method you use, the Action Center opens. Figure 2 shows an example. I clicked the arrow button to the right of each heading so that you can see the descriptive text under each heading. You can click that button to show or hide the same descriptive text.

By default, Windows Firewall is turned on and working at all times, so your Action Center should show "On" beside the Firewall item, as in Figure 2 (and you will see only the Network Firewall item in Action Center if you click the arrow beside the Security heading). If yours shows Off or Not Monitored, it might be because you have a third-party firewall program running in place of Windows Firewall. There are many such programs available, such as McAfee, Symantec (Norton), Gibson Research, and other companies. If your firewall is turned off and you don't know why, it would be good to find out — perhaps from your computer manufacturer or someone who knows. If you don't have any firewall up, you should definitely turn on Windows Firewall.


There is no advantage to having two or more firewalls running simultaneously. In fact, more than one firewall is likely to cause unnecessary problems.

2.1. Turning Windows Firewall On or Off

To turn Windows Firewall on or off, you must have administrative privileges. In the System and Security Control Panel window, click Windows Firewall. You should see the current firewall status in the right pane, and options for controlling the firewall in the left pane. Click Change Notification Settings or Turn Windows Firewall On or Off in the left pane to see the options shown in the foreground of Figure 3.

Use the Block All Incoming Connections check box only to temporarily disable exceptions when connecting to public Wi-Fi networks. You can find more on that topic in the sections to follow.

Figure 2. Action Center.

Figure 3. Settings for Windows Firewall.

If you have a third-party firewall that you feel is more secure than the Windows Firewall, you can choose the Off option to turn off Windows Firewall. Just make sure you have a firewall up when you go online. Otherwise, you won't have anything to stop uninvited traffic on your network connection.

If you have a firewall at home, such as a wireless access point (WAP) or a cable or DSL modem that provides firewall features, and those features are turned on, you can safely turn off Windows Firewall. However, there usually is no downside to leaving Windows Firewall turned on even when an upstream firewall is in place. The exception is when you are trying to play multiplayer games or accomplish networking with other computers on the network and can't get the ports right in Windows Firewall to make it work. In these situations, just turn off Windows Firewall on the computers (but make sure your upstream firewall is working)!

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