Hi. My name is Maile Ohye. I’m a senior support engineer at Google. Have you ever wondered how websites remember your user name and password every time you visit? Or how online stores know which items you’ve added to your shopping cart? What makes these and other customized online experiences possible are cookies.
So what is a cookie? It’s a small file that websites place on visitors’ browsers. The information in the cookie file travels back and forth between the browser it’s stored on– say Firefox or Internet Explorer– and the websites the browser visits.
Why? Cookies allow the sites you visit to recognize your computer when you return and then tailor your online experience accordingly. It’s a lot like the claim check you get from the dry cleaners.
When you come back for your clothes, the person working there uses the number on your claim check to make sure they give you the right stuff. In the same way, when my cookie tells Google that I visited its site before, Google is able to remember my preferences, like the fact that I want to see my search results in English, or that I’ve turned on SafeSearch, a tool that blocks adult content from my search results.
What else do cookies do? On weather sites they remember which cities you want the forecast for. On e-commerce sites they make sure all your selections are in your virtual shopping cart when you go to check out. And on finance sites they allow you to easily track your stock portfolio without having to re-enter the information every time you visit.
As you can see, cookies can save you a lot of time and hassle. And like a claim check, a cookie ID is usually just a combination of letters and numbers. Most of the time there’s no personally identifiable information in a cookie file. No name, email address, or phone number.
And cookies cannot be used to run programs on your computer, access information on your hard drive, or deliver viruses. But that’s not the whole cookie story. There are different types of cookies. A first-party cookie is the kind of cookie I just told you about. A cookie that goes back and forth between your browser and the website you’re visiting, allowing that website to store information about your preferences.
Third-party cookies work a bit differently. Unlike first-party cookies that travel back and forth between your browser and the website you’re visiting, third-party cookies typically travel between your browser and the website of a company that’s displaying an ad on the site you’re visiting.
That’s why they’re called third-party cookies. Because the website sending cookies to your browser, usually an ad-serving company, is actually a different site from the one you’re visiting.
Ad-serving companies use third-party cookies to remember what ads have already appeared on your browser. Like the fact that you clicked on an ad for a new Sony Playstation game and saw the same Nintendo ad twice. This information helps advertisers deliver ads that are relevant to your interests, control the number of times you see a given ad, and measure the effectiveness of ad campaigns.