What Do Cookies Do?
Cookies don't actually do anything. They are simply small pieces of stored information that you have provided during your visit to a website.
Example 1: First Party Cookie
If you opted to allow cookies on this website it would have set a 'persistent' cookie called 'CookieCompliance' and an expiry date 30 days from when you clicked the button. Providing that your browser isn't set to block cookies that is! More on that later...
This cookie does nothing by itself, but the code (scripts) behind the pages do. They check to see if the cookie has been set, and if so, they hide the cookie compliance notice so you don't have to keep clicking the accept button on every page. If you decided not to allow the cookie, or your browser is set to block it, you will continue to see the notice at the top of every page.
Why do we use a persistent cookie? This allows us to remember your choice if you return to our website (within 30 days), and saves you having to allow cookies for this website on every visit. Note: this does not apply if you access the website from a different PC or device, or even a different browser, as cookies are stored locally.
This is just one example of a simple 'First Party Cookie' (i.e. it is only set and read on this website). Many websites also make use of 'Third Party Cookies', which can be of more concern to some people.
Example 2: Third Party Cookie
This website makes use of Google Analytics to analyse our website traffic. This helps us improve the website by
seeing what content our visitors are most interested in. This requires the following (third party) cookies:
__utma (expires after 1 year)
__utmb (expires after 30 mins)
__utmc (expires at end of session)
__utmz (expires after 12 hours)
By using these cookies, Google can create reports for us which prove invaluable to improving our website content. NO personal information is gathered, other than tracking your movements through our website.
Another popular use of third party cookies by many websites is to track browsing behaviour in order to serve up targeted advertising, or to track advertising campaigns. This type of usage is considered by some to be an 'invasion of privacy' and is the biggest point of contention.
In order to help clarify the Information Commissioner's Office (ICO) implementation of the cookie law, the International Chamber of Commerce (ICC) have categorised cookies into four groups: Strictly Necessary, Performance, Functionality, and Targeting/Advertising.
See Is my website compliant? for an explanation of these categories.