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HTG Explains: What’s a Browser Cookie?

We’ve recently been hearing about tracking cookies and laws in the European Union forcing websites to explain their use of cookies to their visitors. If you’re wondering what cookies are and what all the fuss is about, you’re not alone.

Cookies are an important browser feature – if you disable cookies, you’ll find yourself unable to log into websites. While cookies have important, good uses, they also have more questionable uses.

What’s a Browser Cookie?

Cookies are small pieces of information websites store on your computer. Cookies only contain bits of text, not anything else. The text can be a user ID, session ID, or any other text. For example, web pages can be configurable – a web page could have a Hide link that hides a certain element on the page. The page can save this setting on your computer with a cookie. When you load the page in the future, the page can examine the cookie and automatically hide the element.

If you clear your cookies, you’ll be logged out of all websites and websites won’t remember any settings you’ve changed on them.

Cookies are very common – you probably have hundreds or even thousands stored in your browser right now.

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How Cookies Work

Your web browser stores and manages cookies. You can find a list of websites storing cookies and view the cookies themselves – although it’s usually not interesting to look at the content of the cookies – in your browser’s settings. If you use multiple web browsers on your computer, each browser has its own set of cookies.

Websites are only allowed to look at their own cookies – for example, when you visit How-To Geek, we can’t examine cookies from other websites. This prevents malicious websites from snooping and stealing your login sessions.

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Good Uses for Cookies

As we’ve seen, 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.

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“Bad” Uses for Cookies

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.

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Tracking networks can also use the data for other purposes – for example, selling aggregated browsing data to others.

Managing Your Browser’s Cookies

You can manage your browser’s cookies from its settings window. Each browser’s Clear Private Data tool will also delete cookies. For information on viewing and clearing your browser’s cookies, see our article on deleting cookies in the five most popular browsers on Windows.

One problem with clearing cookies is that it will log you out of sites you use. If you want to stay logged into the websites you use but block other websites from using cookies, check out our guide to blocking all cookies except for the sites you use. Bear in mind that some websites won’t work properly if you disable cookies for them.

Chris Hoffman is a technology writer and all-around computer geek. He's as at home using the Linux terminal as he is digging into the Windows registry. Connect with him on Google+.

  • Published 07/20/12

Comments (13)

  1. Anon

    I saw nothing about LSO’s, “Super Cookies,” etc. So perhaps this might help (too):

    chrome://bprivacy/content/BetterPrivacy.html

    Yes. It’s the web page for the Firefox add-on Better Privacy. But have you actually read it? Read it!

  2. r

    mmmmmm….chocolate chip cookies

  3. abubasim

    Chocolate chip browser cookies… om-nom-nom… :)

  4. James Ford

    >>If you clear your cookies, you’ll be logged out of all websites and websites won’t remember any >>settings you’ve changed on them.

    I believe you should have said “If you clear your cookies, the next time you connect to a site you will have to re-enter your logon credentials and other settings for sites that require them.”

  5. Barry Dunwell

    After over 20 years frustration with MS and windows have now converted to iMac …G…d what a refreshing difference, I,ve always found your site most helpful and informative..So would it be possible to include Mac features in your emails..Many thanks Baz

  6. Jim

    http://www.Keebler.com sends cookies to your computer.

  7. Johnny Brown

    Yeah, what about these new tracking cookies that AVG Internet Security 2012 can’t remove some new ones from Microsoft.

  8. Cathleen Caffrey

    WHAT ABOUT 3RD PARTY COOKIES?

    Your explanation of regular cookies is pretty clear. However, neither here nor anyplace can I find a reason why some programs/sites DEMAND 3rd party cookies to work. Most sites this doesn’t matter – I won’t go to a site that requires this. But some, including a bank, say they HAVE to have that clicked as OK in order for certain bank functions to work properly. Other programs I use regularly have the same requirement.

    None of the programs requiring this seem to have any good reason to allow my cookies to be transferred to a 3rd party. One vendor said to turn off the 3rd party cookies but add their site as an exception. Thee is NO exception feature for 3rd party cookies, so if you OK third party cookies, you have to allow ALL 3rd party cookies – or so all the helps and experimentation with various settings seem to say. (It didn’t work for my bank, for example.)

    I’d really appreciate an article about how 3rd party cookies are used for reasons other than allowing other advertisers to have one’s information. This is REALLY FRUSTRATING. I’d also like to know if anyone is working on some protection for customers – eg. having browsers allow a 3rd party exception list as well as a regular exception list.

    Thanks.

  9. BigDom

    I use a plugin called Ghostery which both shows and blocks tracking cookies.
    Some web pages have more than 15 tracking cookies at a time.
    For example Ghostery has told me it has blocked 5 cookies on this page.
    They are:-
    1. Google Adsense
    2. Google Analytics
    3. Lotame
    4. Quantcast
    5. ScoreCard Research Beacon

  10. M Henri Day

    Several browsers, e g, Firefox, offer settings that allow one to inform webistes that one doesn’t want to be tracked. A free 3rd-party application which blocks tracking and which works very well for me, is Do Not Track Plus, which is available from Abine. On this page, it prevents 2 social networks, 3 ad networks, and 6 companies from tracking me. Not bad !…

    Declaration : Other than as a user, I have no connexion whatever with the company….

    Henri

  11. Anonymous

    In real life, too many cookies are bad for you cause they can make you fat and susceptible to all kinds of health problems, not the least of which might be diabetes. One or two cookies might be good. But consuming any baked good like a crack addict or that famous Sesame Street Muppet is not so good. It’s also not good to consume every browser cookie too.

    You would also be well advised to check other browser items like plugins and add-ons since outdated things like Java and Flash are much more likely to cause you much bigger headaches than any browser cookie will. But you still need to be constantly be on top of the cookie situation if for no other reason than tracking and potential data leaks too. And if you’re the type to say, “I don’t care if they track me” then you’re just burying your head in the sand.

    But like anything, moderation is key. And that might be a clue for anyone who doesn’t regularly do a little system-wide house cleaning and/or maintenance. Cookies are just one of many things that need attention.

    And apps like CCleaner do help but they’re not going to do everything. You still need to deal with anti-virus / anti-malware (AV/AM) as well as constantly keep things updated. Configuring your browser to deny pop-ups, deny 3′d party cookies, deny tracking, and never saving passwords (or form data) might also help. And that’s just for starts! But again, it’s not everything. Even the mere act of being online without a browser may require some kind of fancy proxy routing just so certain “entities” don’t track you or somehow “hack” your system. It’s getting ridiculous!

    But it’s just more hoops we all have to jump through I suppose. It almost makes me want to go back to the days of simple TTY terminals on a local BBS where the worst thing I had to worry about was getting scammed by some Nigerian wanting financial assistance.

  12. r

    mmmmmmmmm…more chocolate chip cookies

  13. AD

    Hello Chris,

    How do I contact you via email?

    Thanks,
    AD

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