When I wrote Memories and Cookies for Byte several years ago after the dot-com boom went bust, I got pushback from the editor. Why would anyone care about persistence, monitoring and cookies structures? As a Director at one of those Internet datacenter companies at the height (and fall) of the bubble, I knew that cookies were very important to bizdev and sales as an indicator to tracking unique visitors. Of course, the underlying assumption was that cookies were persistent even though browsers allowed one to selectively delete them. On my modern Firefox browser there is even a special “remove all cookies” button that makes non-flash cookie removal a snap (flash cookies, aka local shared objects in flash-speak, are persistent objects embedded in the flash plug-in, and not removed by the browser’s cookie mechanism; this is one reason lots of sites are going to flash). And remove them we do — up to 1/3 of computer users remove cookies at least once per month, according to comScore, and 7% of computers account for 35% of all cookies served.
While not surprising, this has serious implications for ad monetization.