How Internet Cookies Work

Internet cookies are information stored as text strings on a machine by a web server. Most commonly, cookies are used to store user IDs.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how Stuff Works dot com
where smart Happens. Hi, I'm Marshall Brain with today's question,
what is an Internet cookie? Cookies have for some reason
gained a rather sinister image, but they're really simple and harmless.

(00:25):
A cookie is just information stored as text strings on
your machine by a web server. A web server sends
you a cookie, and the browser stores it on the
hard disk. The browser then returns the cookie to the
server the next time the page is referenced. The most
common use of a cookie is to store a user

(00:45):
I D. For example, a cookie might contain the following
string I D equals nine six three five. Amazon dot
com is one site that uses this technique. When you
order a book, you fill out a form with your
name address. Amazon assigns you an i D in its database,
stores your information with that i D on its server,

(01:08):
and sends the i D to your browser as a cookie.
Your browser stores the i D on your hard disk.
The next time you go to Amazon, the idea is
sent back to the server. The server looks you up
by your I D and customizes the web page that
sends back to you. In essence, it knows who you
are so it can say welcome back, Joe Smith. You

(01:29):
might be wondering, is there any more to cookies than that. No,
they are simply text strings stored on the hard disk.
They are little text files. You can open them up
and see the strings that are being saved. There's nothing magic,
there's nothing complicated about it. Our cookies harmful? No, They're
just short text strings, and they can often make browsing

(01:52):
better by allowing a server to recall any customized information
you've set our cookies comment. Yes, the typical machine has
hundreds of separate cookies on the hard disk. Can cookies
transmit computer viruses? No, they're just text strings. Can accompany
read your personal information from your hard disc with a cookie? No?

(02:15):
Only the cookie that is sent in the first place
is returned to the server. It's not modified or manipulated
in any way. Be sure to check out our new
video podcast, Stuff from the Future. Join How Stuff Work
staff as we explore the most promising and perplexing possibilities
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(02:36):
Download it today on iTunes.