Cookies

Quite simply put, cookies are small bytes of data dropped from a website onto your computer - so it can identify you for the next time you visit that site.

The most common use of cookies in todays websites, is google analytics and this is what is used on the website you are visiting. Below is a summary of cookies used by Google Anlytics (last updated 18th April 2018), but for the most up to date details please visit https://developers.google.com/analytics/devguides/collection/gajs/cookie-usage)

 

Overview

Google Analytics is a simple, easy-to-use tool that helps website owners measure how users interact with website content. As a user navigates between web pages, Google Analytics provides website owners JavaScript tags (libraries) to record information about the page a user has seen, for example the URL of the page. The Google Analytics JavaScript libraries use HTTP Cookies to "remember" what a user has done on previous pages / interactions with the website.

Important: Read the Google Analytics privacy document for more details about the data collected by Google Analytics.

Google Analytics supports three JavaScript libraries (tags) for measuring website usage: gtag.jsanalytics.js, and ga.js. The following sections describe how each use cookies.

 

gtag.js and analytics.js – cookie usage

The analytics.js JavaScript library is part of Universal Analytics and uses first-party cookies to:

When using the recommended JavaScript snippet, gtag.js and analytics.js set cookies on the highest level domain they can. For example, if your website address is blog.example.co.uk, analytics.js will set the cookie domain to .example.co.uk. Setting cookies on the highest level domain possible allows users to be tracked across subdomains without any extra configuration.

Note: gtag.js and analytics.js do not require setting cookies to transmit data to Google Analytics.

gtag.js and analytics.js set the following cookies:

Cookie Name

Expiration Time

Description

_ga

2 years

Used to distinguish users.

_gid

24 hours

Used to distinguish users.

_gat

1 minute

Used to throttle request rate. If Google Analytics is deployed via Google Tag Manager, this cookie will be named _dc_gtm_<property-id>.

AMP_TOKEN

30 seconds to 1 year

Contains a token that can be used to retrieve a Client ID from AMP Client ID service. Other possible values indicate opt-out, inflight request or an error retrieving a Client ID from AMP Client ID service.

_gac_<property-id>

90 days

Contains campaign related information for the user. If you have linked your Google Analytics and AdWords accounts, AdWords website conversion tags will read this cookie unless you opt-out.Learn more.

 

Customization

Read the analytics.js Domains & Cookies developer guide to learn all the ways these default settings can be customized.

Read the Security and privacy in Universal Analytics document for more information about Universal Analytics and cookies.

 

ga.js – cookie usage

The ga.js JavaScript library uses first-party cookies to:

By default, this library sets cookies on the domain specified in the document.host browser property and sets the cookie path to the root level (/).

This library sets the following cookies:

Cookie Name

Default Expiration Time

Description

__utma

2 years from set/update

Used to distinguish users and sessions. The cookie is created when the javascript library executes and no existing __utma cookies exists. The cookie is updated every time data is sent to Google Analytics.

__utmt

10 minutes

Used to throttle request rate.

__utmb

30 mins from set/update

Used to determine new sessions/visits. The cookie is created when the javascript library executes and no existing __utmb cookies exists. The cookie is updated every time data is sent to Google Analytics.

__utmc

End of browser session

Not used in ga.js. Set for interoperability with urchin.js. Historically, this cookie operated in conjunction with the __utmb cookie to determine whether the user was in a new session/visit.

__utmz

6 months from set/update

Stores the traffic source or campaign that explains how the user reached your site. The cookie is created when the javascript library executes and is updated every time data is sent to Google Analytics.

__utmv

2 years from set/update

Used to store visitor-level custom variable data. This cookie is created when a developer uses the _setCustomVar method with a visitor level custom variable. This cookie was also used for the deprecated _setVar method. The cookie is updated every time data is sent to Google Analytics.

 

Customization

The following methods can be used to customize how cookies are set:

Read the Tracking Multiple Domains guide to learn how to configure ga.js to measure user interaction across domains.

 

urchin.js – cookie usage

Historically, Google Analytics provided a JavaScript measurement library named urchin.js. When the newer ga.js library launched, developers were encouraged to migrate to the new library. For sites that have not completed the migration, urchin.js sets cookies identically to what is set in ga.js. Read the ga.js cookie usage section above for more details.

 

Google Analytics for Display Advertisers – cookie usage

For customers that are using Google Analytics' Display Advertiser features, such as remarketing, a third-partyDoubleClick cookie is used in addition to the other cookies described in this document for just these features. For more information about this cookie, visit the Google Advertising Privacy FAQ.

 

Content Experiments - cookie usage

For websites using Google Analytics content experiments, the following cookies are used for these features in addition to the other cookies described in this document:

Cookie Name

Expiration Time

Description

__utmx

18 months

Used to determine a user's inclusion in an experiment.

__utmxx

18 months

Used to determine the expiry of experiments a user has been included in.

 

Optimize 360 - cookie usage

For websites using Optimize 360, the following cookie is used in addition to the other cookies described in this document:

Cookie Name

Expiration Time

Description

_gaexp

Depends on the length of the experiment but typically 90 days.

Used to determine a user's inclusion in an experiment and the expiry of experiments a user has been included in.