How It Works: Cookies
It's nice to be recognized. On the Web, sites can greet you like an old
friend thanks to
When you visit a site that sets cookies, commands embedded in the page
cause your browser to contact the site's server. The server sends information
back to the browser, where it's stored in a particular place on your hard
drive. Different browsers store cookies in different places: Netscape Navigator
maintains a file called
Cookies come in two varieties: Session cookies and persistent cookies. Session cookies clear out after you close the browser window (ending the session) and often are used by "shopping carts" at online stores to keep track of items you want to buy. Persistent cookies are set by news sites, banner ad companies, and others who want to know when you return to a site. These files reside on your hard drive after you leave the site.
Both types of cookie files contain the URL or domain name of the site you visited and some internal codes that indicate which pages you visited. Persistent cookies add the last time you visited the site and how many times you've been there. They usually contain a code that becomes your unique identifier, which lets a site know that you've been there before. Some cookies can contain personal information, such as a name or e-mail address, but only if you've given that information to the Web site. Contrary to popular rumor, cookies can't "steal" your name or e-mail address if you don't give it out.
If you surf the Web, you likely have plenty of cookies on your hard drive. Nearly all commercial Web sites (including PC World.com) set cookies, as do noncommercial sites that carry advertising. Probably the only sites that won't prompt your browser for cookies are personal home pages that don't carry ads and originate on local or regional Internet service provider servers. Cookies are often fewer than 100 bytes, so they won't affect your browsing speed. But because browsers are set to accept cookies by default, you may not know one has been placed; if you are concerned about your privacy, you may want to avoid sites that use them.
Cookies perform myriad functions for both Web surfers and Web sites. For
the user, they make the Web more convenient. Sites that require registration,
such as the
For businesses, cookies can play a role similar to that of a salesperson.
Some shopping sites, such as
Some consumer groups claim that cookies have a dark side: reduced user privacy. Cookies track where you've been and what you've looked at on the Web. A visit to a single site can result in several cookies, and not all of the cookies report back directly to the site you are visiting: Some send the information to the site's advertisers. Cookie Central, a clearinghouse for cookie information, states that some Web advertising companies, including FocaLink and DoubleClick, surreptitiously set cookies that report back directly to them and keep track of your cookies with a database. By cross-referencing various cookies they have on you, they can profile your interests, spending habits, and lifestyle to target-market products to you. And as Net advertising companies grow and buy out related firms--as DoubleClick recently did with direct-marketing agency Abacus Direct--more people are growing concerned about how information gathered through cookies will be used. Using data Abacus may have on you, such as your name and address, DoubleClick could use its cookies, which contain a record of your surfing habits, to create a profile of your activities.
You do have a say in this: Browsers include features to block cookies. Both Communicator and IE let you disable cookies completely or will prompt you when a cookie is being set. Communicator includes an option to accept only cookies that get sent back to the originating server. But because some sites contain so many cookies, it's often not worth being notified: You could spend a lot of time approving or denying cookie requests.
Instead of using your browser to block them, you can run utilities that
remove cookies from your hard drive, such as