What Are Cookies?
Ok, let's get the obvious stuff out of the way first. We are talking about HTTP cookies, also known as web cookies or browser cookies here. If you came to this website looking for some sort of recipe for biscuits, I'm afraid you've come to the wrong place ;-)
Web cookies are simply small pieces of data sent between a website and your browser. Many of these are temporary (session) cookies that are deleted when you close your browser. Longer term (persistent) cookies are stored on your PC or SmartPhone/PDA as small text files.
Session cookies are typically used for things like signing in to a members area, adding items to a shopping cart, or enhancing your viewing experience.
Persistent cookies are used to remember your choices, e.g. customising your location on weather-related websites, automatically signing you in to a social media website, etc. These will expire at a pre-determined date unless manually deleted by yourself. See Can I control Cookies? for more info on these.
Here is a brief overview of cookies from Maile Ohye, Senior Support Engineer at Google:
Most cookies are related to the website (domain) that you are visiting, however Third Party cookies have become much more common in recent years. These are cookies used by other websites other than the one you are visiting. Common examples are Google Analytics (helps website owners analyse the traffic on their website), and Facebook 'Like' buttons (remembers your recommendation). For more information on third party cookies, see What do Cookies do?
The information stored in cookies is very simple and contains a number of 'name', 'value' pairs of data, e.g. 'Username', 'Jeff'. For security reasons the data field is often encrypted, so instead of containing the real name it would contain something like '7f15f1ad99c489dc0314952535e424d5'. There is a limit to the number and size of cookies that a website can serve, and they can ONLY store information that you have provided.
Cookies have been around for a long time (since 1994 to be precise), however they have often been mis-understood and given a dubious reputation by the press.
What Cookies Are Not...
- Cookies are NOT programs!
- Cookies CANNOT open programs, contain viruses or malware.
- Cookies CANNOT secretly scour your PC for personal or sensitive information.
Most browsers will allow you varying levels of control over cookies, including blocking them completely. Take a look at Can I control Cookies? for further information.