Routers, firewalls give PCs extra hack-attack protection

August 12, 2004|By Mike Himowitz

ONCE UPON a time, I could devote most of my column inches to the cool things people can do with computers. Today, I spend too much time telling people how to defend their PCs against online muggers. "Sometimes I think you've turned into a police reporter," a longtime colleague joked.

Two recent columns about spyware, for example, brought a barrage of additional questions about Internet security - and a surprising number about routers and firewalls.

Routers and firewalls are basic online bodyguards, and if you have a broadband connection, you should use both. By themselves, they won't protect you from viruses, worms and spyware. But they can keep intruders away and help prevent gremlins that do sneak through from compromising your PC and personal information.

Before we discuss firewalls and routers, it's a good idea to know a little bit about how the Internet works - but don't worry, we'll keep geek-speak to a minimum.

Every computer connected to the Internet has a unique numeric address theoretically visible to every other computer. This Internet Protocol (IP) address is usually expressed as a series of four numbers separated by periods, such as

This addressing system is the key to the power of the Internet - it's the reason why it's as easy to connect to a computer in Tasmania as it is to one across town.

Internet service providers assign IP addresses to their customers. Home users typically have IP addresses assigned on the fly whenever they dial in to an ISP such as America Online or Earthlink, or when they first connect their PCs to broadband cable or DSL modems.

Because the Internet was designed in a more innocent age as an open system for sharing both information and computing resources, the Internet Protocol makes it easy for machines to communicate.

When one computer wants to talk to another, it sends a message to the receiving machine's IP address, and the other machine responds.

Typically, computers use different communications channels, known as ports, for different purposes, such as Web browsing, e-mail, file transfer, or instant messaging. The problem, in this age of malicious hackers, is that without any type of security, outsiders can take advantage of these channels and flaws in the computer's operating system to poke around in your files, steal information, plant mischievous programs, or even take control of your PC. This is particularly true if you have file or printer sharing enabled on a local network.

How does an intruder find you? Typically with software that scans IP addresses looking for a basic response (known as a "ping") and then probing for "open" ports that respond to commands or requests for information. Computers running Microsoft Windows have proved particularly vulnerable to these attacks - note the monthly security patches that Microsoft issues to plug these holes. But other operating systems have vulnerabilities, too.

Most vulnerable are PCs connected to the Internet directly through a cable or DSL modem, particularly if they're left running 24 hours a day.

That's where routers and firewalls come in. They work together to minimize the danger, and their features often overlap.

A router is designed to connect one network to another. The typical home router is a small box with four to six connections for network cables and often a wireless antenna that allows computers with wireless adapters to join the network.

As its name implies, the router passes Internet information packets along the proper path to their destination, like a train or truck dispatcher. But routers designed for the home and small offices also allow multiple PCs to share an Internet connection. Typically, you'll connect one or more computers to the router and plug the router into your cable or DSL modem.

Once installed, a router serves as a "front man" for all the computers on the local network behind it, even if the "network" consists of a single machine. The router contacts the ISP, obtains a single IP address for the whole network and passes information to the proper PC on the inside. It also allows computers on the home network to share information without going through the Internet.

Although they can be configured to block or pass different types of data packets, most routers are set up by default to hide the ports that hackers access. The router allows outside packets through only from communications sessions your computer initiates - such as sending e-mail, browsing the Web, or starting an Internet chat program.

This is also one of the basic functions of a firewall. In real life, a firewall is a fireproof barrier that separates one structure or room from another to keep a blaze from spreading. In the virtual world, it's a piece of hardware or software that provides additional levels of protection from outsiders. Some routers have firewalls built in to protect an entire network, but typical home firewalls are built through software that protects a single PC.

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