SID on adwords.google.co.uk
About this cookie:
This is a very common cookie name but where it is found as a session cookie it is likely to be used as for session state management.
This cookie is used by Google in combination with HSID to verify a Google user account and most recent login time.
About this cookie’s host: This domain is owned by Google Inc. Although Google is primarily known as a search engine, the company provides a diverse range of products and services. Its main source of revenue however is advertising. Google tracks users extensively both through its own products and sites, and the numerous technologies embedded into many millions of websites around the world. It uses the data gathered from most of these services to profile the interests of web users and sell advertising space to organisations based on such interest profiles as well as aligning adverts to the content on the pages where its customer's adverts appear.
Related general information about SID:
These cookies are used to deliver adverts more relevant to you and your interests. They are also used to limit the number of times you see an advertisement as well as help measure the effectiveness of the advertising campaign. They are usually placed by advertising networks with the website operator's permission. They remember that you have visited a website and this information is shared with other organisations such as advertisers. Quite often targeting or advertising cookies will be linked to site functionality provided by the other organisation.More about cookie classifications.
Third Party Cookies
If the host domain for a cookie is different to the one in the browser bar when it was downloaded, then it is a third party cookie.
They are usually placed in a website via scripts or tags added into the web page. Sometimes these scripts will also bring additional functionality to the site, such as enabling content to be shared via social networks.
For example, if you visit a site that has a YouTube video in one of its pages. This has been included by the website owner, using a piece of code provided by YouTube. YouTube will then be able to set cookies through this code, and know that you have watched that video, or even just visited the page the video is in.
Online advertising is the most common use of third party cookies. By adding their tags to a page, which may or may not display adverts, advertisers can track a user (or their device) across many of the websites they visit.
This allows them to build up a 'behavioural profile' of the user, which can then be used to target them with online ads based around their 'calculated' interests.
Analytics cookies are probably the most common form of persistent cookies in use today.