Cookies monitor your browsing and these small pieces of code are downloaded and stored by your browser when you visit certain websites. Cookies are responsible for the spooky effect where an advert for an e-commerce site you’ve visited subsequently appears on a totally different site.
Cookies can be cleared from your browser at any time: look for options such as Clear History or Clear Browser Data in the settings. And thanks to new European Union rules, websites now have to ask your permission to send a cookie. Don’t be too hard on cookies, though: they also do useful tasks such as remembering your preferences and sign-ins for sites.