Nov 7, 2018

How Google Analytics tracking works

The GA tracking cookies on the third-party site will be first party cookies so they are less likely to be rejected by the browser.

The GA transfers the visitor’s cookie values from one domain to another via the query string.

To track users on a website Universal Analytics uses a first party cookie, just like the previous version of Google Analytics.
After Google Analytics code gathers information about each pageview, the information is sent in the query string of a request for the __utm.gif file. This file is requested for every single pageview, transaction and event. When the files are processed, Google Analytics can then string together the individual actions into a visit.

References:
http://cutroni.com/blog/2006/06/25/how-google-analytics-tracks-third-party-domains/
http://cutroni.com/blog/2013/03/21/tracking-website-with-universal-analytics/
https://developers.google.com/analytics/resources/concepts/gaConceptsTrackingOverview?hl=es-ES
Universal Analytics: The Next Generation of Google Analytics