__utmc on www.ustream.tv
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This is one of the four main cookies set by the Google Analytics service which enables website owners to track visitor behaviour and measure site performance. It is not used in most sites but is set to enable interoperability with the older version of Google Analytics code known as Urchin. In this older versions this was used in combination with the __utmb cookie to identify new sessions/visits for returning visitors. When used by Google Analytics this is always a Session cookie which is destroyed when the user closes their browser. Where it is seen as a Persistent cookie it is therefore likely to be a different technology setting the cookie.
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Related general information about __utmc:
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