Before you look in more detail at what threats you face and how you can protect yourself against these threats by using a firewall, take a minute to look at your network and establish how much it is worth to you. The best way to establish the value of something is to evaluate the cost of a loss. Take a look at some different types of damage and consider the cost of each:  Lost data: How important is the data on your corporate network? To answer this question, try to estimate what would happen if the data disappeared. Imagine that someone managed to break into your network and deleted all your accounting data, your customer list, and so on. Hopefully you have methods in place to restore lost data from a backup — no matter how you lose it. But, for just a second, imagine that all your corporate data is gone and you have to reconstruct it. Would your company still be in business if this happened to you tomorrow?  Confidential data: If anyone were to break into your network and get access to confidential data — for example, the secret plans for the perpetual motion machine that you are developing — imagine what could happen. What would an intruder do with the data? Because you don’t know, you have to assume the worst. If the secret plans end up in the hands of a competitor, he or she may beat you to the market with a miracle e machine, and the profits and the Nobel Prize in Physics go to that person instead of you. The damage may even be worse if the data that is stolen is your entire customer list, including complete contact and billing information.  Downtime: Have you ever called a company to order an item or to complain about something, and you were told, “I can’t help you, the network is down.” If so, you probably remember your reaction. The excuse sounded cheap, and you felt like taking your business somewhere else. Just because you’re paranoid . . .