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. Open source software puts companies in a terrific position to re-brand and re-position themselves in a market that they may have not been able to reach before. In the business world, open source is all about image and when consumers witness corporations contributing (instead of selling) to the buying public, they gain big favor in the eyes of their users (plus tremendous opportunities to sell other items). 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. Although the malicious code that this person generated may have worked for a small percentage of users, sufficed to say, the online service continued on and still exists today. Despite his motivation or intention, his efforts were null. We wouldn't be surprised to learn if other motivations behind spreading viruses were similar to this person's, but that doesn't justify the damage that viruses do. But this didn't stop the batch file fever that started under MS-DOS - and in some small circles, batch files are still as popular as they were in the beginning. Even though you may use Windows XP or Vista, batch files can save you tons of time by automatically starting multiple programs and performing different tasks at the single click of a button. Nicotine and tar mean certain death when it comes to computer fans, however should you find a need to clean the fan, do so with extreme care. It's quite easy to cause more damage from cleaning so if you're not comfortable with cleaning your PC yourself, take it to a shop for servicing. Otherwise, you can unplug and disassemble the computer to do it yourself.