The following cookies are set by Google Analytics:
A persistent cookie – remains on a computer, unless it expires or the cookie cache is cleared. It tracks visitors. Metrics associated with the Google __utma cookie include: first visit (unique visit), last visit (returning visit). This also includes Days and Visits to purchase calculations which afford ecommerce websites with data intelligence around purchasing sales funnels.
__utmb Cookie & __utmc Cookies
These cookies work in tandem to calculate visit length. Google __utmb cookie demarks the exact arrival time, then Google __utmc registers the precise exit time of the user. Because __utmb counts entrance visits, it is a session cookie, and expires at the end of the session, e.g. when the user leaves the page. A timestamp of 30 minutes must pass before Google cookie __utmc expires. Given__utmc cannot tell if a browser or website session ends. Therefore, if no new page view is recorded in 30 minutes the cookie is expired. This is a standard ‘grace period’ in web analytics. Omniture and WebTrends among many others follow the same procedure.
Cookie __utmz monitors the HTTP Referrer and notes where a visitor arrived from, with the referrer siloed into type (Search engine (organic or cpc), direct, social and unaccounted). From the HTTP Referrer the __utmz Cookie also registers, what keyword generated the visit plus geolocation data…