In line with recent changes in European legislation, UK law now requires website operators to ask for a website user's permission when placing certain kinds of cookie on their devices for the first time. Where consent is required, the law states that it should be "informed consent". This increases the onus on websites to ensure that visitors understand what cookies are and why website operators and others want to use them.

The Information Commissioner's Office (ICO) has published detailed guidance on the law and a number of other organisations have published information about the use of cookies by businesses.

Business organisation the International Chambers of Commerce (ICC) has also published advice regarding the cookie law.

Below is some reference information on cookies and the categories they fall into.

What is a cookie?

Cookies are text files containing small amounts of information which are downloaded to your device when you visit a website. Cookies are then sent back to the originating website on each subsequent visit, or to another website that recognises that cookie. Cookies are useful because they allow a website to recognise a user's device. You can find more information about cookies at: www.allaboutcookies.org and www.youronlinechoices.eu for a video about cookies visit www.google.co.uk/goodtoknow/data-on-the-web/cookies

Cookies do lots of different jobs, like letting you navigate between pages efficiently, remembering your preferences, and generally improve the user experience. They can also help to ensure that adverts you see online are more relevant to you and your interests.

Cookie Categories

Category 1: strictly necessary cookies

These cookies are essential in order to enable you to move around the website and use its features, such as accessing secure areas of the website. Without these cookies services you have asked for, like shopping baskets or e-billing, cannot be provided.

No user consent is required for category 1 cookies.

Examples include:

• Remembering previous actions (e.g. entered text) when navigating back to a page in the same session.
• Managing and passing security tokens to different services within a website to identify the visitor's status (e.g. logged in or not)
• To maintain tokens for the implementation of secure areas of the website
• To route customers to specific versions/applications of a service, such as might be used during a technical migration

Category 2: performance cookies

These cookies collect information about how visitors use a website, for instance which pages visitors go to most often, and if they get error messages from web pages. These cookies don't collect information that identifies a visitor. All information these cookies collect is aggregated and therefore anonymous. It is only used to improve how a website works.

Consent for cookies in this category, according to the ICC, can be obtained by placing appropriate wording in the site Terms and Conditions (most professional sites will have this already). So, no opt-in required.

Examples include:

• Web analytics — where the data collected is limited to the website operator's use only, for managing the performance and design of the site. These cookies can be third-party cookies but the information must be for the exclusive use of the publisher of the website visited.
• Ad response rates — where the data is used exclusively for calculating response rates (click-through rates) to improve the effectiveness of advertising purchased on a site external to the destination website. If the same cookie is used to retarget adverts on a third-party site this would fall outside the performance category (see Category 4)
• Affiliate tracking — where the cookie is used to let affiliates know that a visitor to a site visited a partner site some time later and if that visit resulted in the use or purchase of a product or service, including details of the product and service purchased. Affiliate tracking cookies allow the affiliate to improve the effectiveness of their site. If the same cookie is used to retarget adverts this would fall outside the performance category (see Category 4)
• Error management — Measuring errors presented on a website, typically this will be to support service improvement or complaint management and will generally be closely linked with web analytics.
• Testing designs — Testing variations of design, typically using A/B or multivariate testing, to ensure a consistent look and feel is maintained for the user of the site in the current and subsequent sessions.

Category 3: functionality cookies

These cookies allow the website to remember choices you make (such as your user name, language or the region you are in) and provide enhanced, more personal features. For instance, a website may be able to provide you with local weather reports or traffic news by storing in a cookie the region in which you are currently located. These cookies can also be used to remember changes you have made to text size, fonts and other parts of web pages that you can customise. The information these cookies collect cannot track your browsing activity on other websites.

Examples include:

• Remembering settings a user has applied to a website such as layout, font size, preferences, colours etc.
• Remembering a choice such as not to be asked again to fill in a questionnaire.
• Detecting if a service has already been offered, such as offering a tutorial on future visits to the website.
• Providing information to allow an optional service to function such as offering a live chat session.
• Fulfilling a request by the user such as submitting a comment.

Category 4: targeting cookies or advertising cookies

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.

Examples include:

• Cookies placed by advertising networks to collect browsing habits in order to target relevant adverts to the user. The site the user is visiting need not actually be serving adverts, but often this will also be the case.
• Cookies placed by advertising networks in conjunction with a service implemented by the website to increase functionality, such as commenting on a blog, adding a site to the user's social network, providing maps or counters of visitors to a site.