Confirming seeming odd data coming from companies relying on cookie tracking, a new Jupiter Research study showed that two out of five users wind up having their cookies deleted at least once a month. Many marketers and certainly marketing technology firms have come to rely on the ubiquitous cookie to measure ad performance, conduct frequency caps on ads, gauge audience size and innumerable other basic metrics. But in a study of about 2,300 users, 10 percent said they deleted their cookies each day, 17 percent did so each week, and 12 percent did it monthly. Consumers generally deleted their cookies for fear of invasions of their privacy, and tended not to understand the convenience aspects of persistent cookies - like not having to log in each time visiting many websites. Interestingly, 28 percent of web users are rejecting cookies on a selective basis, targeting cookies like those placed by third party ad serving networks. This could make the tracking of latent visits and transactions very difficult, requiring marketers to extrapolate how many of each they may be missing due to cookie elimination.