COOKIES WE USE
Globally and in the European Union member states Google sets the following cookies:
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).
__utmb Cookie & __utmc Cookie
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.
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).
This cookie lasts six months.
Google __utmv Cookie lasts "forever". It is a persistant cookie. It is used for segmentation, data experimentation and the __utmv works hand in hand with the __utmz cookie to improve cookie targeting capabilities.