The most important new medium of mass communication of the past 40 years was not in any way connected with television, moving pictures, or the recording industry; it initially emerged, instead, as a project of the U.S. Defense Department. In the 1960s, the depart-ment's Advanced Research Projects Agency, in coordination with several research institutions, came up with a system for connecting or "networking" distantly located computers using independent, dedicated telephone lines. Researchers using the system experimented with sending simple text messages to one another over the network. Soon, the trickle of research-oriented messages and data became a tidal wave of information exchange of all kinds. The new medium of "electronic mail" eventually changed the way we interact with our friends, co-workers, and families. It also brought our everyday reality much closer to Marshall McLuhan's pipedream of a genuine worldwide community rooted in technology.

The practice of sending electronic...