What exactly is a cookie?

A cookie is a small data file that is sent from a website to your device, and stored on its hard drive or mobile browser. A cookie typically contains two bits of data: a unique ID for each user, and a site name. Cookies enable websites to retrieve this information when you revisit them, so that they can remember you and your preferences and tailor page content for you based on this information.

For example, websites might use cookies to make specific personalised recommendations based on your previous online browsing and buying behaviour. They might also use cookies to offer to remember information such as user names and passwords for sites you visit often, so that you don’t have to spend time filling them in each time you log on.

Cookies are simply data files and not programs. They can retrieve only the data that they have stored on your device. They can’t access any other information about you from your device.

What do cookies do?

Cookies are useful for quickly transferring information from one visit on a website to the next visit, or visits between related sites, without needing to store huge amounts of data on a server.

On your first visit to a website, the site server downloads a cookie on to your device. If you visit the site again, your device will search to see if it has an associated cookie, read it and relay the data it contains back to the website. The website will then recognise you as a previous visitor and remember any personal information that you shared with that site, such as:

• account user names and passwords;
• your email address;
• prior purchases you made;
• items you viewed;
• your preferred settings and themes.

The web server can then use that information to serve you with relevant web-page content.

Cookies make it easy for websites to collect precise user-specific information about their visitors. This generally makes it simpler for you to navigate the web and enjoy a personalised experience.

Many cookies do essential jobs. For example, web servers use authentication cookies to determine who you are when you try to log into an account. Other types of cookies enable you to shop online, storing items as you add them to your virtual shopping basket.

Cookies can be either temporary (session cookies) or persistent (permanent cookies).

Session cookies are stored in your device’s temporary memory – not on your hard drive – while you’re browsing a website. Usually these cookies are deleted when you close the browser. If you were to reopen the browser and revisit the website, the site would not ‘remember’ that you had visited previously. Session cookies remain active only until you leave a site.

Persistent cookies remain stored on your hard drive, persisting from session to session until you delete them or they reach a set expiration date. Persistent cookies can store log-in details, bookmarks, credit card details and preferred settings and themes - resulting in a faster and smoother web journey.

Because persistent cookies can log your uniquely identifiable movements online over a long period, they are sometimes called tracking cookies. Third-party tracking is frequently used by advertisers to find out what websites you visit and the content you view, as well as other information. Third-party cookies are set when you visit a site that contains an embedded ad from another (third-party) website. Advertisers can embed ads in a large number of sites, collate the information their cookies gather and use it to send you ads tailored to your interests.

Are cookies safe?

Cookies themselves aren’t harmful, but they can carry sensitive personal data – and that makes them potential targets for hackers. Cookie theft is a risk if you sign into a site using public WiFi, as session cookies are not encrypted. A hacker can copy the cookie data and use it to impersonate you and get into your account. It doesn’t happen often, but it’s a risk to be aware of.

Because tracking cookies – particularly third-party tracking cookies – can be used without your knowledge or permission to put together a detailed profile of you, you may consider this tracking to be an invasion of privacy. You may also object to being sent targeted adverts. Other people might find such ads helpful.

How can I manage my cookies?

Most browsers will allow you to control your cookie settings. You can choose to enable or disable cookies, see what cookies your device has stored, delete cookies, or choose how long they are stored on your device. Click on the relevant link to find out how to manage cookies in Firefox, Internet Explorer 11, Chrome, Safari and Opera.

How can I keep my cookie information safe?

You can actively help protect your cookie files with these easy-to-follow tips:

• Install comprehensive Internet security software across your devices.

• Be careful about sharing personal information, particularly on public computers.

• Don’t use public WiFi to access social media accounts, online banking or shopping sites. Don’t send private or sensitive information on untrusted WiFi.

• If you must use public WiFi, consider using a Virtual Private Network (VPN). A VPN allows you to create a private ‘virtual tunnel’ on a public network.

• If you don’t want your browser to save temporary files and cookies and your browsing history, use the privacy mode. Here’s how to do so in Firefox, Internet Explorer, Chrome, Safari and Opera.

• Use browser add-ons to customise your cookie preferences. There are a huge number of free extensions that can block ads and disable third-party tracking.

• Remember to log out of all accounts when you’ve finished.

Be a smart cookie

Cookies make our experiences on the Internet more efficient – be it online shopping, autofilling addresses, logging into frequently used accounts, or being offered recommendations for products or services we might like. Without cookies, doing just about anything on the Internet would be far more cumbersome.

Because they sometimes handle sensitive private data, cookies can also be considered a security risk. They can also be used to build online profiles of you and tailor targeted ads, which you might consider to be an invasion of privacy. However, armed with the information and tips above you can take control and do your best to protect yourself from intruders.

Go on, tame that cookie monster.