Security fears are driving more than half of all internet users to routinely delete cookies on their computer, which is making it difficult for legitimate websites to monitor visitor behaviour.
JupiterResearch carried out research among thousands of website consumers and found that 58% have deleted cookies from their machine and 39% are deleting all cookies from their PCs on a monthly basis.
Cookies are small files used by commercial sites to track the behaviour of visitors, to enable them to offer what they feel are the most appropriate products or services the next time a visitor logs onto the site. They are also used to recognise registered website users.
But privacy and security concerns are encouraging consumers to disable cookies on their browsers or delete them after they have been downloaded, said JupiterResearch.
"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," said Eric Peterson, analyst at JupiterResearch.
"Because personalisation, 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," he added.