That dot and group of three letters is known as an "extension," and the extension explains what kind of file it is. A file could be a plain text file, an image, a sound, a video, or program. But without seeing the extension, you wouldn't know it unless you double-clicked on it. The following list defines some of the most common extensions that you'll find on your computer. Known as viruses, worms, or spyware, this malicious code can destroy important files and render your computer good for only one thing: sending sensitive data back to the server of an identity thief. 2. Don't store sensitive data on your computer in the first place. Should your computer get infected with a virus, worm, or piece of spyware, you can thwart the individuals responsible by not storing your personal information on your PC so that when and if your computer does send back data - it won't be anything valuable. Most main menus display themselves as soon as a device is turned on, so chances are that if you're standing before a device that shows a bunch of choices to do something, you're looking at a main menu. The buttons on these main menus of course take you to additional menus, which in turn give you even more choices to make. Since we're describing a home network that will connect to the Internet, you're strongly advised to install a protective firewall program to thwart Internet viruses, worms, or other damaging spyware code. Firewalls prevent - but they don't repair. Only anti-virus and anti-spyware programs can reverse damage. These extras aren't included with "what comes out of the box," and the only way to get them is to accessorize. To illustrate the importance of accessorizing, we like to use the "plain dough" analogy. Let's say that a brand new computer is a batch of plain dough - waiting to be flavored and baked into something useful. We suspect that today's "computer illiterates" are people who haven't taken the time to experiment with such a machine. And we strongly believe that spending just twenty minutes with one could turn the most adamant technological caveman into any one of those who have fun wreaking chatroom havoc on the Internet today.