Since the late 1990s, outbreaks of malicious computer viruses and worms like LoveLetter have grown increasingly common and have caused billions of dollars in damage and lost productivity. Where do these invasive programs come from? How does the computer industry combat these threats? What are the legal implications of writing or distributing malicious computer software?

Invasive Software Overview

Invasive programs (i.e. viruses, worms, and Trojan horses) are constructed using the same basic computer logic that underlies traditional application programs such as games, word processors, or spreadsheets. Like other programs, invasive software must be written by people, and it must be intentionally designed and programmed to perform specific actions.

Invasive programs act without the computer user's knowledge or permission and may cause a variety of intentional and unintentional damage. Viruses, worms, and Trojan horses that cause intentional damage to computer systems are said to...