Some people deliberately work at the task of destroying computers, and they perform their dirty deeds by installing viruses on your computer. Other nasty folks invade your computer while you're on the Internet, and they get private information from your files (or leave viruses on your computer).
Fortunately, you can protect your network from these Internet hackers by purchasing and installing a firewall. A firewall is a program that protects computers from users on other networks (remember, the Internet is another network). In fact, a firewall can protect computers from other computers, but if you have a network, you don't want to isolate your computer from the other computers on your network.
Windows XP comes with a built-in firewall, but if you have a home network, you can't use the Windows XP firewall unless you've installed the service pack SP2. (More on that shortly.)
What a firewall does
The firewall blocks communication in both directions - to and from the Internet. A firewall works by watching everything that happens on your computer that has anything to do with activity outside your computer. Unless you say that it's okay, no action can occur between your computer and another computer. That other computer could be on the Internet or on your network.
Because the firewall stops any computer from accessing your computer, you must configure the firewall software to accept communications between your computer and the other computers on your network. Doing so frees the firewall to concentrate on communications between your computer and a computer on the Internet.
Any computer that tries to access your computer is either stopped dead in its tracks or is stopped temporarily until you tell the firewall whether to let the computer gain access (depending on the way you configure the firewall's behavior).
Computers send and receive data via ports. When an intruder attempts to reach your IP address, it's really your communication ports that are being examined. In addition to the visible ports, such as your USB, your computer contains thousands of virtual ports. You can't see a virtual port because it's a software service rather than a physical connector. However, as does a physical port, a virtual port accepts and sends data.
Examining a firewall's log file
After you install a firewall program on your network, open your firewall's log file (a list of all the attempts made to access your computer) and look at the information (a command exists on the menu bar of the firewall software to accomplish this). All the computers that have tried to get into your computer are listed by their IP addresses. Go to one of the Web sites that provides reverse lookups; these sites allow you to enter an IP address, and they return the name of the offending computer.
Sometimes the IP address belongs to an Internet service provider (ISP), and it's part of a range of addresses that are assigned to that ISP. This means that a customer of that ISP, who has been assigned that IP address for his or her Internet session, is trying to get into your computer. You probably won't be able to determine the identity of the customer. However, you can notify the ISP that at a certain time on a certain date, this particular IP address was trying to break in to your computer, and the ISP can determine to whom the address was assigned at that moment. Ask the ISP to let you know what it does to resolve the problem.
You can't tell whether a snooper was trying to do some damage, either by leaving behind a virus or stealing personal information. You can only tell that the snooper has tried to hack into your computer.
Hardware firewalls in routers
If you're sharing an Internet connection, and you're using a cable or DSL modem, the easiest, most efficient, and most powerful way to share the connection is to install a router.
You can buy routers that have built-in firewalls. The firewall-enabled router sits between your modem and the rest of your network, separating the Internet and your network into two independent, unconnected networks (sort of like two armed camps). The only device that's seen from the Internet is the router, which has a firewall. All the computers on the network are invisible to the Internet.
Several router manufacturers offer routers with firewall protection, and the equipment is available with a wide variety of options. Here are some of the manufacturers who offer hardware firewall devices:
* Linksys.com
* D-Link.com
* Belkin.com
* NetGear.com
Using firewalls with Windows XP
If you've installed a software firewall, or you're using the Windows XP SP2 firewall, you'll have to disable a router's firewall. This is one case in which "the more the merrier" doesn't work.
If you haven't installed Service Pack 2 (SP2) for Windows XP, turn off the Windows XP Internet Connection Firewall (ICF) and either install a software firewall program or use a router with a firewall feature, as discussed previously. To turn off ICF, follow these steps:
1. Choose Start --> Control Panel --> Network and Internet Connections --> Network Connections.
The Network Connections folder opens, displaying an icon or listing for your Internet connection(s).
2. Right-click the Local Area Network Connection, and choose Properties.
The Properties dialog box for your connection opens.
3. Click the Advanced tab, and deselect the option to use ICF.
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