Utma, utmb, utmz cookies

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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
__utma
through
__utmz
are stored by websites that choose to use Google Analytics to see how people use their websites.

(Assuming it's purely analytics cookies, which is presumable, you don't need to worry about them. Worry about ad-net cookies like Facebook's instead)


The cookie names seem to come from an earlier versions called the Urchin Tracking Module.

The names are still used by the newer ga.js.


Some details:

  • __utmz records whether the visitor came from, one of:
a search engine (and if so, the search keyword used)
a link, or
from no previous page (e.g. a bookmark, or a typed-in URL)
  • __utma stores
the amount of your visits
the time of the first visit, the previous visit, and the current visit
  • __utmb and __utmc are used to approximate how fast people leave, by recording 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.


Also:

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