Respawning Cookies
Ashkan Soltani erklärt die technischen Hintergründe von schwer zu löschenden Cookies.
What differentiates KISSmetrics apart from Hulu with regards to respawning is, in addition to Flash and HTML5 LocalStorage, KISSmetrics was exploiting the browser cache to store persistent identifiers via stored Javascript and ETags. ETags are tokens presented by a user’s browser to a remote webserver in order to determine whether a given resource (such as an image) has changed since the last time it was fetched. Rather than simply using it for version control, we found KISSmetrics returning ETag values that reliably matched the unique values in their ‘km_ai’ user cookies.
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As explained above, KISSmetrics uses the same identifier for consumers across the different websites it serves. In addition to data enhancement, this practice may be problematic because it enables KISSmetrics to uniquely track individuals across sites they visit. This makes KISSmetrics’ position more similar to a network advertiser than an analytics provider.

