Good Uses and Bad Uses for Cookies

Cookies have a number of very important uses. The web wouldn’t be what it is without them today.

• Cookies store your login state. Without them, you wouldn’t be able to log into websites. Websites use cookies to remember and identify you.
• Cookies store preferences on websites. You couldn’t change settings and have them persist between page loads without cookies.
• Cookies allow websites to provide personalized content. For example, if you’re shopping on Amazon, Amazon can remember the products you’ve browsed and recommend similar products – even if you’re not logged in.

However, cookies can also be used for more questionable purposes. Advertising and tracking networks use tracking cookies to track you across the web. When you visit website that uses scripts from an advertising network, that network can set a cookie in your browser. When you visit another website that uses tracking scripts from the same network, the advertising network can check the value of your cookie – it knows the same person visited both websites. In this way, the advertising networks track you across the web.

This information is used to target ads to you – for example, if you search for car insurance and later visit a news website, you may see advertisements for car insurance on the news website. The advertisements may not be related to the website you’re currently on, but they will be related to the websites you were visiting before. Depending on the advertising network, you may be able to opt out of this – as with the Google Ads Preferences page, which also shows the advertising categories you’ve been assigned by Google based on the websites you’ve been tracked across. Tracking networks can also use the data for other purposes – for example, selling aggregated browsing data to others.