A cookie is a text file with a small bit of information in it, which a server downloads onto your computer, tablet or smartphone when you visit a website. Then you can be recognised when you come back, or when you visit another site which recognises that cookie.
Different types of cookie do different things. Some let you navigate between different pages on a website. Some remember your website preferences. Some give you adverts tailored to your interests. And some measure how many sites or which you visit. Session-based cookies sit on your device while you're on a website then expire once you shut your web browser. Persistent cookies stay on your device for longer, then automatically expire.
The law says we have to give you details about the cookies we use and why we use them. We also have to have your consent to use them. So we've developed a system of classifying the different types of cookie we use on bt.com, or that third parties might download to your device via our websites. Our cookie classification system explains how we use the cookies, and also determines how we ask for your consent to use them. We also explain what functionality you lose if you decide you don't want to have them on your device.
To keep things simple we split out the types of cookies we use into different categories. You can select which types of cookies you want to have on your device at any one time. At the footer of every page there is a link to change your cookie settings at any time. Each category is accompanied by a description of what type of actions it performs.
Some cookies are 'strictly necessary' for us to give you the online service you've asked for. We don't ask for your permission to use these and all the information collected by those cookies is anonymous and doesn't in any way affect your privacy. We use 'performance' cookies to measure how our websites perform so we can improve our pages and measure how that works for visitors.
You can't disable 'strictly necessary' or 'performance' cookies and by using our website and online services, you're automatically agreeing to have those on your device.
We also give a list of the individual cookies we use in each category in the 'Find out more about cookies' section. That's so if you check your internet settings, you know what these are if you've agreed we can use them. You can always take cookies off your device using your browser settings. But if you do, some things won't work as well – for example, lots of pop up boxes might run the same ads, or you mightn't be able to get to a page you earlier personalised.
Your browser options let you choose whether to accept, not to accept or be warned before accepting cookies. (They're in the advanced preferences section.) Our cookie categorisation is also used in a 'cookie code' developed by the International Chamber of Commerce to help website operators stick to the rules.