Cookies are small files associating your browsing habits with an ID that's assigned to your web browsers.
They can't identify you, specifically (your name, age and gender, for example), but they can be used to infer likely data about your interests and demographic.
Look at a pair of shoes on one website, and you might start to see adverts for similar footwear appear to follow you around the web.
Browser settings for controlling cookies
All web browsers have the ability to turn off cookies, although turning them off altogether is usually overkill, and will lead to some sites simply not working properly.
For example, if you blocked all cookies via your web browser, the Which? website would not be able to recognise you as a logged-in member, forcing you to log in your details repeatedly.
Accepted practice suggests blocking third-party cookies is the best approach. This still allows the type of functional cookies that websites need to use, and are typically harmless.
How to block cookies
Cookie settings in Google Chrome
From the Tools menu (three horizontal lines in the top-right of Chrome), click Settings then (right at the bottom) click Show advanced settings and then the button marked Content settings. Tick the box marked Block third-party cookies and site data.
Cookie settings in Internet Explorer
In Internet Explorer, head to Internet Options via the Tools menu. Click on the Privacy tab and there’s a slide bar for altering the level of cookie control, from allowing anything to blocking everything.
Cookie settings in Firefox
In Firefox, click on Tools, then Options, then Privacy, where you'll find an option for disabling third-party cookies.
How to clear existing cookies
Preventing third-party cookies stops companies from dropping new snooping tools, but there's likely to be a bevy of files already on your computer, which you may want to remove.
You can do this through the Options menu in Internet Explorer, the Tools drop-down in Google Chrome and Options and Privacy tabs in Firefox.
Note: deleting all cookies will remove pre-filled data fields such as usernames and passwords for websites.
EU cookie controls
The Which? website uses no third-party cookies. The cookies we do use are only necessary for functions like remembering if you’re logged in, or monitoring page-visits to see which of our review areas are proving popular.