HTTP and HTML, the standards that created the graphical, hyperlinked Web, are open and simple. Any participant can see the source code for any Web page. That makes it a risky place for critical business applications. To bring real world safety to the Web requires added control and security. Some programmers have been wreaking havoc with code since they figured out they could.
Viruses are the most common manifestation of coders gone bad.
Pre-Internet viruses were restricted in scope. The results, though irritating, could be localized and eradicated. The Internet changed the nature of viruses as profoundly as it is changing everything else. Viruses are free to flash around the globe, infecting victims at an astronomical rate. Spoofing Web sites is an easy task.