Jupiter Media Press Release
This of course affects all kinds of web operations from tracking, affiliate marketing and behavioural targetting - Jupiters Niki Skevak says that an entirely new way of capturing consumer behaviour will have to be invented.
I presume that cookie deletion comes from automated spyware removal and the like, as i can't imagine putting that figure down to manual deletion, but it's a worrying statistic for many marketers...
This, from the release:
The report found that as many as 39% of online users may be deleting cookies from their primary computer monthly, undermining the usefulness of cookie-based measurement and leaving many site operators flying blind. "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 at 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," added Peterson.
Privacy and security concerns on the part of online users are responsible for the cookie-deletion behavior that JupiterResearch has found. According to a recent consumer survey cited in the report, 52% of online users indicate a strong interest in stories and articles about Internet security and privacy, while 38% of online users believe that cookies are an invasion of their security and privacy online and 44% of online users believe that deleting or blocking cookies will protect them.