A guide to internet cookies, the small files that store information about your online activity

• Cookies, also known as «HTTP cookies,» are small text files that websites store on your computer to help track your activity.
• Most cookies are used to track what sites you’re logged in to, and your local settings on that site.
• Third-party cookies pose the greatest risk to your privacy because they track your activity across websites.
• Visit Insider’s Tech Reference library for more stories.

The internet as we know it today would be impossible without cookies – small data files that store information about your online activity. These files are used by websites to remember you, keep you logged in between sessions, know your preferences, and more.

You can think of cookies like a dry-cleaning receipt. When you drop off your clothing, you get a slip of paper that describes how many items you’re leaving behind and how they should be cleaned. When you come back days later, that receipt is the key to getting your things back the way you intended.

Nearly every website stories cookies of some sort, and the amount that they store is only going up. Here’s everything you need to know about «HTTP cookies,» or simply «cookies.»

The different types of cookies

Cookies fall into two broad categories: session cookies and persistent cookies. Here’s the difference between them.

Session cookies

These are temporary cookies that reside in your computer’s temporary memory – they are never stored on your computer’s hard drive.

They’re only used to help your web browser navigate around a website and remember the previous pages you’ve visited.

Persistent cookies

These are cookies that are stored long-term on your computer’s hard drive. Some are there essentially forever; others are set to expire after a set period of time.

Regardless, persistent cookies are responsible for important details like remembering your login credentials so you stay logged in between visits, and personalization details about how you’ve configured specific sites.

Some persistent cookies are known as third-party cookies. These cookies track your online activities across the internet, like the pages you’ve visited and products you’ve looked at. Generally, it’s these persistent third-party cookies that are responsible for compromising your privacy.

Why do we have cookies?

The term «cookie» sometimes obfuscates what it really is – a simple text file stored on your computer to make browsing the internet easier.

As a general rule, cookies are saved onto your computer while you’re visiting a website and stored locally on your computer. When the website needs a reminder of who you are – like when you’re trying to load your shopping cart, for instance – it reads the cookies on your computer.

This way, the website doesn’t need to track and manage a huge number of users; all that data is stored locally on each user’s computer. This makes browsing a site faster and easier for all parties involved.

The risks of using cookies

While the simplicity and convenience of the modern internet can be largely attributed to the use of cookies, there are some risks associated with them. That risk varies based on the cookies.

First-party cookies are created and used by the website you are using. These are the session and persistent cookies described earlier in the article that track your site navigation, login information, and preferences. They’re generally considered safe and useful.

Third-party cookies are generated by a site or advertisement and have the ability to track and record your activities long after you leave that first website. These cookies make it possible to serve you ads on Facebook for a product you looked at minutes, days, or weeks earlier on a completely different retail site.

Some third-party cookies are even worse: Called zombie cookies, they’re installed even if you’ve set your browser preferences to prevent third-party cookies, and resist being deleted – or can reappear after being removed. They can be difficult or impossible to eradicate.

How to manage cookies

You can use the internet without cookies, though your experience will be much less convenient. All major web browsers make it possible to delete the cookies stored on your computer on demand. See our article on how to clear cookies for major browsers in Windows, for example. Likewise, you can learn how to clear cookies on your iPad, iPhone, and Mac.

You can also choose to block persistent cookies so new ones can’t be stored. But it’s important to remember that not all cookies are bad or a risk to your privacy. Many browsers also let you separately enable and disable third-party cookies, so you can allow first-party cookies (which are the most useful ones) but disable third-party tracking cookies when possible.

How to opt out of website cookies with WebChoices and avoid targeted adsHow to clear cookies on your Windows 10 computer in 3 different browsersHow to clear and manage cookies on your Mac computer’s Safari browserHow to enable cookies on an Android device in Google Chrome to save your data and optimize your web browsing

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