Cookies are pieces of data, normally stored in text files, that websites place on visitors’ computers to store a range of information, usually specific to that visitor – or rather the device they are using to view the site – like the browser or mobile phone.
They were created to overcome a limitation in web technology. Web pages are ‘stateless’ – which means that they have no memory, and cannot easily pass information between each other. So cookies provide a kind of memory for web pages.
Cookies allow you to login on one page, then move around to other pages and stay logged in. They allow you to set preferences for the display of a page, and for these to be remembered the next time you return to it.
Cookies can also be used to watch the pages you visit between sites, which allows advertisers to build up a picture of your interests. Then when you land on a site that shows one of their adverts – they can tailor it to those interests. This is known as ‘behavioural advertising’.
Cookies are incredibly useful – they allow modern websites to work the way people have come to expect – with every increasing levels of personalization and rich interactive functionality.
However, they can also be used to manipulate your web experience in ways you might not expect, or like. It could be to your benefit, or the benefit of someone else – even a business or organization that you have never had any direct contact with, or perhaps heard of.
There are many different types and uses of cookies, but most can be classified in a number of different ways.
One of the key attributes of a cookie is its ‘Host’ – this is the domain name of the site that ultimately sets the cookie. Only the host domain can retrieve and read the contents of the cookie once it has been set.
If the host name is the same as the domain in the browser address bar when it is set or retrieved, then it is a First Party Cookie.
First party cookies are only set or retrieved by the website while you are visiting it, so they cannot normally be used to track activity or pass data from one site to another.
However the owner of that website can still collect data through their cookies and use that to change how the website appears to the user, or the information it displays.
Most desktop browsers allow you to see a list of the cookies that have been set – and they will normally be listed by the host domain value.
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.
Session Cookies are only stored temporarily in the browser’s memory, and are destroyed when it is closed down, although they will survive navigating away from the website they came from.
If you have to login to a website every time you open your browser and visit it – then it is using a session cookie to store your login credentials.
Many websites use session cookies for essential site functions, and to make sure pages are sent to the browser as quickly and efficiently as possible.
As the name suggests, this type of cookie is saved on your computer so that when you close it down and start it up again, it can still be there.
Persistent cookies are created by giving them an expiry date. If that expiry date is reached, it will be destroyed by the computer. If the expiry date is not set then it is automatically a session cookie.
The expiry date will normally be saved as the time the cookie was first created plus a number of seconds, determined by the programmer who wrote the code for the cookie. However, there is no real limit on the expiry date – so it could be set to be 20 years in the future. In addition, if you revisit the website that served up the cookie, it may automatically place an updated version on your computer – with a revised future expiry date.
If you login into a website, then shut down your computer, start it up again, and go back to the website to find you are still logged in – then it is using a persistent cookie to remember you.
Persistent cookies are also used to track visitor behaviour as you move around a site, and this data is used to try and understand what people do and don’t like about a site so it can be improved. This practice is known as Web Analytics. Since Google started providing its own analytics technology free of charge to website owners, almost all websites use some form of it – although there are also paid-for services available to rival Google’s.
Analytics cookies are probably the most common form of persistent cookies in use today.
However, persistent cookies can also, oddly, have a shorter life span than some session cookies, as they can be coded to be destroyed within a second or two of being set, whereas a session cookie will always last until you close down your browser.
Secure cookies are only transmitted via HTTPS – which you will typically find in the checkout pages of online shopping sites.
This ensures that any data in the cookie will be encrypted as it passes between the website and the browser. As you might imagine – cookies that are used by e-commerce sites to remember credit card details, or manage the transaction process in some way, would normally be secure, but any other cookie might also be made secure.
This protects it from so-called cross-site-scripting (XSS) attacks, where a malicious script tries to send the content of a cookie to a third party website.
The term ‘Super Cookie’ (or sometimes Supercookie) is usually applied to tracking technologies that are not regular HTTP cookies and are stored in a different way on a user’s machine.
This makes them harder to find and get rid of – because they can’t be removed using the regular privacy controls found in most browsers.
Adobe Flash applications sometimes use local file storage to optimise performance – and these files, known as Local Storage Objects, can also be used for tracking purposes, so they are sometimes labelled as ‘supercookies’.
So called zombie cookies, are technologies that are used to re-spawn regular http cookies after they have been deleted by users.
The practice of using zombie cookies is clearly intended to circumvent users’ attempts at controlling their privacy, and therefore is widely frowned upon. In many circumstances, the use of zombie cookies would be a breach of privacy laws and regulations. However their use is rare.
Cookies are used in many different ways, and many of them make the web experience much better. However, most of this can be summed up on one word – personalization.
The more you use the site, the more Amazon understands what kind of products you search for and buy. This allows it to make recommendations of products you might like – which could help prevent extensive searching in such a big store.
If you have bought from Amazon and don’t actively sign out from your account, it will remember you when you return – greeting you by name even. It also remembers any items you have put in your shopping basket but not purchased – making it quicker to go through the checkout.
Of course, they are doing it for their own benefit as well – all of this increases their sales, but it does benefit users.
In fact, online shopping would not be possible without cookies. If we didn’t have cookies, you could not effectively login to a website. Instead you would have to tell it who you are every time you went to a new page, which would be extremely tedious.
Cookies can personalize a website in all sorts of other ways as well – without having to be about shopping. For example, they can be used to remember a user prefers a larger font size than normal. A news website might remember that you like certain types of stories and promote them to the home page.
There are also more subtle uses of cookies that bring benefits that are less tangible.
Some services even claim they can work out which part of a page users spend most time looking at, even without clicking anything. This is because they can track where in the page the mouse pointer is, and many users tend to place the pointer near where they are looking at.
Aggregating all that data into useful information is known as ‘web analytics’, and it gives website owners real understanding about how people user their site, which are the most and least popular pages, and how this changes over time. Doing this enables them to improve the site – doing more of what visitors like and less of what they don’t. Ultimately this benefits visitors through better content and services targeted at their needs.
However cookies does also raise a number of privacy concerns that people ought to be aware of.
Almost all modern browsers provide ways for you to control how your computer handles cookies. This includes the ability to block all or different types of cookies – and preventing them from being placed on your machine in the first place. They also enable you to delete the cookies that you already have. However each browser is different – and some offer more fine-grained control than others, or at least control that is easier to find. Anyone wishing to take better control over their online privacy would be well advised to spend some time familiarising themselves with the controls in their browser. However, below we provide a bit of an overview for the most common browsers.
Browsers are of course found on smartphone and tablets as well as traditional computers. Generally speaking smartphone browsers do not provide anywhere near the level of functionality in respect of cookie controls that ones on your PC or laptop do. However this is changing quickly so it is worthwhile trying to find out what controls you can make use of.
Google Chrome provides quite a good level of control over cookies. These can be found under the ‘Settings’ menu, which you can get to by clicking on the spanner icon in the top right hand corner.
Under ‘Advanced Settings’ you can find a section dedicated to Privacy, which includes being able to clear your browsing history – which has several settings options, including deleting all your cookies.
You can also use Chrome to send a ‘Do Not track’ signal to the websites you visit.
However, the ‘Content Settings’ button also gives access to further controls including the ability to list all cookies and delete them individually. This list also includes HTML5 local storage and databases that modern sites sometimes use instead of cookies.
With Firefox you get to the cookie settings by clicking in the menu box in the top left hand corner and selecting ‘Options’. On the pop-up, then select the ‘Privacy’ icon.
With Firefox you can tick a box that tells every website you visit that you do not want to be tracked. This functionality is known as Do Not Track (DNT), however there is no guarantee at the moment that a website will respect that request – and there are no legal requirements for them to do that.
You can also set your preferences for what Firefox will record of your browsing history, including the way it treats cookies. For example, you can choose to accept third party cookies, but have them deleted when you close the browser. Like with Chrome you can also see a list of all the cookies saved and either delete them all or delete just the ones you don’t like.
More recently, the Mozilla foundation have announced that newer releases of Firefox, most likely from June 2013 onwards, will block third party cookies by default.
In most recent versions of Internet Explorer you select the cog icon in the top right corner, choose ‘Internet Options’ from the drop down menu, then select the ‘Privacy’ tab in the pop-up that appears.
IE uses a slider control which you can use to select different levels of privacy, although you can also select the ‘Advanced’ button for a more custom setting for allowing or blocking first and third party cookies.
It also enables you to create lists of sites where you always want to allow or block cookies. However it does not give you the ability to list the cookies you have, or selectively delete them, through this menu.
To do that – you have to use the ‘Developer Tools’, which you can get to either from the cog icon, or by hitting the F12 button on your keyboard. Then select the ‘cache’ menu and view or clear cookies options in the drop down. The problem with this is that have to be on the site in question to do this, and it is not particularly user friendly – most people would be put off by the idea of using the developer tools, because they are not developers!
Under the Internet Options>General tab you also have a tick box that you can set to delete your browsing history when you shut it down. Ticking this will mean all your cookies are deleted when you close your browser.
From Internet Explorer 10 onwards, Microsoft introduced Do Not Track functionality. This will usually have been switched on by default when the browser was first installed. To check your own settings, go to Internet Options>Advanced. Scroll down to the Security Settings, and there you will find a tick box labelled ‘Always send Do Not Track header’. If you tick or un-tick this box, you will need to re-start the browser for the change to take effect.