Utma, utmb, utmz cookies

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Revision as of 19:46, 21 October 2012 by Helpful (Talk | contribs)

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These are primarily notes
It won't be complete in any sense.
It exists to contain fragments of useful information.
The cookies named
are stored by websites that choose to use Google Analytics to see how people use their websites. Which means it tracks visits. (in a way that, relatively speaking, seems less objectionable way than what ad networks do)

The cookie names seem to come from an earlier versions called the Urchin Tracking Module. These cookie names are still used by the newer ga.js.

Some details:

  • __utmz stores whether the visitor came from a search engine, search keyword, or a link
  • __utma stores the amount of visits (for each visitor), the time of the first visit, the previous visit, and the current visit
  • __utmb and __utmc are used to check approximately how fast people leave: when a visit starts, and approximately ends (c expires quickly). If you look at cookie state changes (e.g. using firecookie), you will see these change regularly.


  • __utmv is used for user-custom variables in Analytics
  • __utmk - digest hashes of utm values (verify)