Why Do I Need Firewalls?

Why would someone want to access your home network? Well, for a lot of reasons, ranging from simple theft of the information on your computers to hijacking your computers and using the anonymity they can provide to conduct other illegal activities. It is impossible to list here all the examples, but let's consider two common ones.

First, most people regularly store information, such as e-mail, spreadsheets, and even passwords to online accounts (eBay and PayPal, for example) on their computers. Figure 1-1 shows how a hacker can launch what is called a brute-force attack to gain access to one of your computers. Tools to perform such attacks, which are easily available on the Internet, use dictionary files to repeatedly attempt to guess your password to remotely log in to your computer or to access a shared drive.

Figure 1-1. Sample Brute-Force Password Attack

If left unchecked, hackers can attempt thousands of times until they succeed. When into the computer, they can simply help themselves to whatever information you have stored there.

In the second example, it is not the information itself on the computers the hacker is interested in, but enlisting your computer (probably along with hundreds or thousands of others) into what is called a bot army. Bot armies are when a hacker has taken over control of many computers and then uses the computers for illicit means, such as to attack other computers or corporate websites. Figure 1-2 shows an example of using a bot army to conduct a distributed denial-of-service (DDoS) attack.

Figure 1-2. Sample DDoS Attack

By exploiting a security flaw in the computer's operating system, hackers can install a small program to take remote control of your computer. After doing so on hundreds or thousands of other computers, hackers can then go after their target with a DDoS attack by instructing all the remote-control computers in the bot army to start sending web page requests to a website such as Microsoft.com and repeat the requests as often as possible. If successful, the tens of thousands of requests can cause a spike in the web server and possibly cause it to fail because of overloading. If they cannot cause the server to fail entirely, it might be possible to disrupt or slow down the service to legitimate folks who are trying to access the website.

This is called a DDoS attack. If the attack were conducted from a single computer, the website owners might be able to recognize a pattern and simply block that computer from making future requests. However, if the attack is coming from thousands of people's home computers, how can the website owner distinguish legitimate requests from an attack? That's the point of a bot army: scale, anonymity, and stealth.

We do not pretend to have the answers to why people do such things. Quite frankly, many of them are highly intelligent folks, who for whatever reason have decided to run against society's grain. Regardless of why, they do it; so, it is important for you not to be a victim.