When you listen to the news, you hear about many different forms of electronic infection. The most common are: Viruses - A virus is a small piece of software that piggybacks on real programs. For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce (by attaching to other programs) or wreak havoc. E-mail viruses - An e-mail virus travels as an attachment to e-mail messages, and usually replicates itself by automatically mailing itself to dozens of people in the victim's e-mail address book. Some e-mail viruses don't even require a double-click -- they launch when you view the infected message in the preview pane of your e-mail software [source: Johnson]. Trojanhorses - A Trojan horse is simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk). Trojan horses have no way to replicate automatically. Worms - A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well. In this article, we will discuss viruses -- both "traditional" viruses and e-mail viruses -- so that you can learn how they work and understand how to protect yourself.

Strange as it may sound the computer virus is something of an Information Age marvel. On one hand viruses show us how vulnerable we are -- a properly engineered virus can have a devastating effect disrupting productivity and doing billions of dollars in damages. On the other hand they show us how sophisticated and interconnected human beings have become.