- The online behavior of a small but growing number of computer users in the United States is monitored by their Internet service providers, who have access to every click and keystroke that comes down the line.
The companies harvest the stream of data for clues to a person's interests, making money from advertisers who use the information to target their online pitches.
The practice represents a significant expansion in the ability to track a household's Web use because it taps into Internet connections, and critics liken it to a phone company listening in on conversations. But the companies involved say customers' privacy is protected because no personally identifying details are released.
The extent of the practice is difficult to gauge because some service providers involved have declined to discuss their practices. Many Web surfers, moreover, probably have little idea they are being monitored.
But at least 100,000 U.S. customers are tracked this way, and service providers have been testing it with as many as 10 percent of U.S. customers, according to tech companies involved in the data collection.
Although common tracking systems, known as cookies, have counted a consumer's visits to a network of sites, the new monitoring, known as "deep-packet inspection,"...