Cookie Crunching May Be Pumping Up Web Traffic

April 17, 2007

Internet cookies might not be as reliable an indicator of distinct Web site visitors as previously thought, according to a Monday report from Internet research company comScore.

A growing number of Internet users have taken to erasing their computer's cookies, which are unique identifiers inserted on a user's computer that reveal what Web sites someone has visited. While this might not seem like a catastrophic event, the deletion of these cookies could lead to inflated traffic reports for a particular Web site, according to the report.

Each time a user visits a Web site for the first time that Web site deposits a virtual checkmark, or cookie, onto the user's computer. That cookie prevents the Web site from cataloging repeat visits from the same user, thereby creating a more accurate count of new visitors to a particular online venue. If a user's cookies have been erased, however, that person's computer is registered as a new user when they visit a Web site, even if they have been there hundreds of times before.

ComScore evaluated a first-party Web site and a third party ad server that each receives more than 100 million hits each month.

Researchers found that 31 percent of U.S. Internet users erased their first-party cookies over the course of the month. As a result, Web sites could be inflating their web traffic by as much as 150 percent, according to comScore.

"These 'serial resetters' have the potential to wildly inflate a site's internal unique visitor tally, because just one set of 'eyeballs' at the site may be counted as 10 or more unique visitors over the course of a month," said Magid Abraham, president and chief executive of comScore, in a statement. "The result is a highly inflated estimate of unique visitors for sites that rely on cookies to count their audience."

Report authors found similar totals on the third-party ad server, with approximately 27 percent of users clearing their cookies at least once a month.

Many people think third-party cookies are deleted more often than first-party cookies because "many PC users reset or delete their cookies using security protection programs," Abraham said. "But these findings suggest that selective cookie management is not prevalent."

Comscore officials were not immediately available for comment.

Copyright 2007 by Ziff Davis Media, Distributed by United Press International