JupiterResearch found that in 2004, 58 percent of online users have deleted cookies, which cripples accurate website visitor measurement.

JupiterResearch's report, "Measuring Unique Visitors: Addressing the Dramatic Decline in the Accuracy of Cookie-Based Measurement," found that tracking cookies is a principal means website operators use to track visitors and account for the effectiveness of marketing campaigns. However, according to a JupiterResearch statement, "if users delete cookies, accurate long-term measurement of consumer behavior on the site is severely compromised."

"Given the number of sites and applications that depend heavily on cookies for accuracy and functionality, the lack of this data represents significant risk for many companies," says Eric T. Peterson, analyst, JupiterResearch.

"Because personalization, tracking and targeting solutions require cookies to identify web visitors over multiple sessions, the accuracy of these solutions has become highly suspect, especially over longer periods of time," adds Peterson.

JupiterResearch found privacy and security concerns on the part of online users are responsible for the cookie-deletion behavior.