Defining and Dealing with Web Cookies

A cookie is a tiny little file that's stored on your computer. It contains the address of the Web site and codes that your browser sends back to the Web site each time you visit a page there. Cookies don't usually contain personal information or anything dangerous; they're usually innocuous and useful.

When you browse the Web, the Web server needs to know who you are if you want to do things that require logging in or putting items in a virtual shopping cart or completing any other process that requires that the Web site remember information about you as you move from page to page. The most commonly used trick that allows Web sites to keep track of what you're doing is called setting cookies.

If you plan to shop on the Web or use other Web services, cookies make it all possible. When you're using an airline reservation site, for example, the site uses cookies to keep the flights you're reserving separate from the ones that other users are reserving at the same time. On the other hand, you might use your credit card to purchase something on a Web site and the site uses a cookie to remember the account with your credit card number. Suppose that you provide this information from a computer at work and the next person to visit that site uses the same computer. That person could, possibly, make purchases on your credit card. Oops.

Internet users have various feelings about cookies. Some people don't care about them, and some of folks view them as an unconscionable invasion of privacy. You get to decide for yourself. Contrary to rumor, cookie files cannot get other information from your hard disk, give you a bad haircut, or otherwise mess up your life. They collect only information that the browser tells them about. In both Firefox and Internet Explorer, you can control which sites can store cookies on your computer.

Controlling cookies in Firefox

Choose Tools --> Options, click the Privacy category, and look in the Cookie section. If the Accept Cookies from Sites check box isn't selected, select it. Set the Keep Until option to They Expire. Or, if you want to decide which sites can store cookies on your computer, set Keep Until to Ask Me Every Time. Firefox doesn't give you the option of accepting first-party cookies and refusing third-party cookies, except by configuring it to ask you each time a site wants to set a cookie.

You can specify which sites can and cannot store cookies by clicking the Exceptions button. You can enter the Web addresses that you definitely trust with cookies (like the shopping sites that you frequent) or that you don't trust (like advertising sites).

You can take a look at the cookies on your computer at any time. Click the Show Cookies button and scroll down the list of sites. If you see some that you don't recognize or that sound suspicious, click the Remove Cookies button.

Controlling cookies in Internet Explorer

Use the Tools --> Internet Options command to display the Internet Options dialog box. The cookie controls are on the Privacy tab, so click it. By default, Internet Explorer sets your privacy level to Medium, allowing cookies from the server you contacted but not from third-party servers (ones other than the one that provided the page you're viewing).

Third-party servers usually deliver advertisements and those annoying pop-up and pop-under ads. You can elect to manage them yourself by clicking the Advanced button to see the Advanced Privacy Settings dialog box and then selecting the Override Automatic Cookie Handling check box. The options are shown in this list:

First-party cookies: You can choose to accept, block, or be prompted to choose, although this option gets tiresome very quickly if you encounter a lot of cookies. Some sites can store three or more cookies per page.

Third-party cookies: Just say no to (that is, choose Block) third-party cookies.

Always allow session cookies: This option lets all session cookies through, a type of cookie used to track a single instance of your visit to a Web site. These cookies are commonly used by shopping sites such as Amazon.com, and are harmless.