If you’ve been using a web browser for any length of time, you’ve almost certainly heard the term ‘cookie’, not least since a change in European law required websites to be much more up front about how they are used.

What you may not know, however, is what cookies are exactly and what they’re used for.


A quick history of cookies

Cookies are almost as old as the web itself. Invented in 1994 as a way to retain certain information about what someone was doing on a website between visits, they take the form of small files stored somewhere on your computer by your web browser.

Cookies were created primarily for convenience. When you log into a website such as BT.com, you’ll see an option along the lines of ‘Remember me’.

Tick it and the next time you visit, you won’t need to type your username again — it’ll be stored as a cookie on your PC and filled in automatically. This is why you should only use this on your own computers rather than on shared machines.

So on the face of it, cookies are extremely useful and, even though hundreds of them build up on your PC over time (though not all of them are saved for so long), they take up very little space.

Some people, however, are concerned that cookies, by their very nature, track and share their every online activity.

The good, the bad and the ugly

Since cookies can be saved on your computer between visits to a particular website and even over the course of several days, they can be used to track which websites you visit. Google, for example, uses cookies to track the behaviour of people who visit websites that make use of its web analytics service.

This gives website owners a way to see how someone found their site (such as via a search or a link from another site), which pages on their site they looked at and for how long. This kind of tracking is essentially harmless and helps website owners create sites that better serve their visitors – but not everyone wants their web activity to be tracked in such a way.

[Related article: How to stay anonymous online]

Advertisers also use cookies in a similar way. When someone visits a page that carries a particular ad, the advertiser can drop a cookie onto their PC and track which websites they go on to visit. Again, this is essentially harmless, but might not appeal to everyone.

Keeping cookies off your computer

Cookies are more or less essential for smooth web browsing, but you can control how and when they’re stored on your computer. That law change in 2009 means that websites in Europe must ask permission to store cookies on your PC, so you can always decline the offer when it appears.

You can also change how your web browser handles cookies, from allowing the ones that are more or less essential for day-to-day use, to blocking all of them, regardless of their purpose.

In Internet Explorer, these settings can be found by clicking the cog icon at the top-right of its window, selecting Internet options and then clicking the Privacy tab on the dialog box that appears.

There are also simple steps you can take to remain as anonymous as possible when browsing the web, as explained in our guide to staying anonymous online.