As we said in our earlier introduction, Tracking, a cookie is a bit of data from a web server. (Think of “fortune cookies” you might get after a Chinese meal, with little bits of wisdom inside each one.) Each web browser keeps its own set of cookies. So, if you use several computers — or several different web browsers on the same computer — each of those browsers has a different set of cookies in its “cookie jar” (actually, in the computer’s memory and/or disk).
So, for example, if you set your Google preferences on a particular browser, Google’s web server can set a cookie in that browser to maintain your preferences on that browser. But if you go to another computer, those preferences you just set on the previous computer won’t be set here because Google’s server can’t know that it’s you on that other computer. (Google has no idea where you are in a room.)
Remember that, unless you have a Google Account and you sign in, Google can’t track you as a person. It can only track what’s happened on the particular browser you’re using at the moment. (This is true of other web servers, too: not just Google’s.)
You can remove the cookies from your browser by using cookie management programs or by using controls built into your browser itself. You can also prevent cookies from being set in the first place. Doing so can help to preserve your privacy, but you can also lose the advantages of cookies — such as being able to set preferences.
Each cookie has a name and an expiration date. When a web server sends a cookie, it asks your browser to keep that particular cookie until a certain date and time. These dates can be:
- Some date in the future. This might be a few minutes or a few hours from now (to track something like your shopping cart in an online store). Or the cookie might expire many years in the future — which means the server wants to keep track of your browser for a long time.
- When you close your browser. This is called a session cookie. The next time you start your browser, the session cookies from the previous session will have vanished.
- Some date in the past. This is how the server asks a browser to remove a previously-stored cookie.
As we’ll see in a moment, Google uses a mixture of session cookies and longer-term cookies.
Most web browsers let you prevent a web server from setting cookies. Add-on software can also control cookies. The most sophisticated browsers, such as Firefox, give you a lot of control over cookies.
Your browser probably has a way to remove some or all stored cookies. Doing that will stop most (but not all) tracking that a web server can do. But, of course, you’ll lose the benefits of permanent cookies. For instance, if you have a Google Account, you’ll probably have to sign in again before you use a personalized Google service like Gmail.
If you’re concerned about privacy but also want the advantages of cookies, some browsers have a good compromise: treating some or all cookies as session cookies. That is, if a server asks to store a cookie until next year, your browser can store it as a session cookie instead.
Note: This section is for people who are interested in more technical details of setting cookies. If you aren’t, please skip ahead to the next chapter.
We’ll start by opening Firefox to a blank page and entering
www.google.com as the URL. We’ve configured Firefox to ask before setting each cookie, and we’ve also just used its “Clear privacy data” command to erase all old cookies. As soon as we go to
www.google.com, the server asks to set a cookie:
Notice that the server wants the cookie to expire in the year 2038 and that the cookie’s name is PREF. (This may be where the server “remembers” our Google preferences.) We click the button, which tells Firefox to erase the cookie when we quit the browser. We could also have denied the cookie, though, to see what might happen next. It’s likely that Google will work fine with almost all cookies denied — except the cookie(s) that keep your Google Account settings.
Later, after doing some searches, we decide to sign in. Clicking the Use my choice for all cookies from this site” if we didn’t want to answer any more questions about
After more searches, we open the Firefox Options dialog to look at the stored cookies. (That’s the little right-hand window in the next screen shot.) Google has set several cookies by now: five for
www.google.com, one for groups.google.com, and at least one more for images.google.com. Clicking on one of the cookies shows that it’s the PREF cookie set two screen shots previous. You generally won’t need to get to this level of detail — but it is possible to, say, remove the stored cookies from a server so that server can’t “remember” you.
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