New York -- Major U.S. Web sites are increasing the number of so-called tracking tools that collect personal details on behalf of marketers, the Wall Street Journal said.
The newspaper said some sites will be capable of planting more than 100 such tools at a time on the computers of visitors that allow real-time surveillance of their activities and generate detailed databases of consumer preferences.
The Journal said its investigation focused on 50 Web sites accounting for about 40 percent of U.S. page visits. A dozen sites, including Comcast.net and MSN.com, installed more than 100 such tracking files on test computers. Google and similar sites also use a plethora of tracking files to develop targeted advertising.