The Web Bug FAQ
by Richard M. Smith (firstname.lastname@example.org)
November 11, 1999
Web Bugs Basics
1. What exactly is a Web Bug?
A Web Bug is a graphics on a Web page or in an Email message that is designed to monitor who is reading the Web page or Email message. Web Bugs are often invisible because they are typically only 1-by-1 pixel in size. They are represented as HTML IMG tags. For example, here are two Web Bugs recently found on Quicken's home page (www.quicken.com):
2. Why are Web Bugs invisible on a page?
<img src="http://ad.doubleclick.net/ad/pixel.quicken/NEW" width=1 height=1
<IMG WIDTH=1 HEIGHT=1 border=0
The two Web Bugs were placed on the home page by Quicken to provide "hit" information about visitors to DoubleClick and MatchLogic (AKA, preferences.com), two Internet advertising companies.
To hide the fact that monitoring is taking place.
3. Are Web Bugs always invisible on a page?
Not necessarily. Any graphics on a Web page that is used for monitoring purposes can be considered a Web Bug.
4. Are all invisible GIF images, Web Bugs?
No. Invisible GIF files are also used for alignment purposes on Web pages. A Web Bug will typically be loaded from a different Web server than the rest of the page, so they are easy to distinguish from alignment GIF files.
5. What other names are Web Bugs known by?
The Internet advertising community prefers the more sanitized term "clear GIF". Web Bugs are also known as "1-by-1 GIFs" and "invisible GIFs".
6. What information is sent to a server when a Web Bug
7. What are some of the uses of a Web Bug on a Web page?
- The IP address of the computer that fetched the Web Bug
- The URL of the page that the Web Bug is located on
- The URL of the Web Bug image
- The time the Web Bug was viewed
- The type of browser that fetched the Web Bug image
- A previously set cookie value
Ad networks can use Web Bugs to add information to a personal profile of what sites a person is visiting. The personal profile is identified by the browser cookie of an ad network. At some later time, this personal profile which is stored in a data base server belonging to the ad network, determines what banner ad one is shown.
8. Where can I find Web Bugs being used?
9. How can I see a Web Bug on a page?
Another use of Web Bugs is to provide an independent accounting of how many people have visited a particular Web site.
Web Bugs are also used to gather statistics about Web browser usage at different places on the Internet.
A Web Bug can be found by viewing the HTML source code of a Web page and searching for IMG tags. A Web Bug will typically have its HEIGHT and WIDTH parameters in the IMG tag set to 1. Also for the tag to be a bug, the image should be loaded from a different server then the rest of the Web page.
Web Bugs in Email Messages
10. What kinds of uses does a Web Bug have in an Email
11. Why are Web Bugs used in "junk" Email messages?
- A Web Bug can be used to find out if a particular Email
message has been read by someone and if so, when the message
- A Web Bug can provide the IP address of the recipient if
the recipient is attempt to remain anonymous.
- Within an organization, A Web Bug can give an idea how
often a message is being forwarded and read.
12. What are some of the Email marketing companies who are
known to use Web Bugs?
13. What companies have used Web Bugs in Email marketing campaigns?
- To measure how many people have viewed the same Email message
in a marketing campaign.
- To detect if someone is viewed a junk Email message or
not. People who do not view a message are removed from
the list for future mailings.
- To synchronize a Web browser cookie to a particular Email
address. This trick allows a Web site to know the identity
of people who come to the site at a later date,
14. What do Web Bugs in Email messages look lile?
- Barnes and Noble
Email Web Bugs are represented as 1-by-1 pixel IMG tags just
like Web Bugs for Web pages. However, because the sender of the
message already knows your Email address, they also include the
Email address in the Web Bug URL. The Email address can be in
plain text or encrypted. For example, here are two Web Bugs
sent to me in junk Email messages:
<img width='1' height='1' src="http://www.m0.net/m/logopen02.asp?
vid=3&catid=370153037&email=SMITHS%40tiac.net" alt=" ">
15. Is there any method of removing Web Bugs from HTML pages?
Not really. The technical problem is that there is no method
of distinguishing Web Bugs from spacer GIFs which are used
on Web pages for aligment purposes. Your best defense against
Web Bugs is to turn off cookies. Instructions for turning off
cookies can be found at the Junkbusters Web site:
16. Why don't Web site privacy policies ever mention Web Bugs?
One note about cookies. Netscape Navigator and
Internet Explorer will still send out existing cookies after
disabling cookies in the browser. You must manually delete
any cookie files on your hard drive to eliminate being tracked
by third-party ad networks.
Good question. Clearly Web site privacy policies need to disclose
the use of Web Bugs as a minimum. Also the general practice of online
profiling by third-party ad networks should be talked about in
privacy policies. However, this important topic is rarely mentioned.
17. Are the use of Web Bugs legal?
A complicated question that is best answered by a lawyer.
18. Are the use of Web Bugs unethical?
Clearly Web Bugs are controversial.
Because they allow people to be monitored, when they don't
expect it, they certainly can be very upsetting.
For example, most people will likely be troubled to learn that an outsider
is tracking when they read Email.
19. Can newsgroup messages be bugged also?
Yes. If someone is using Outlook Express or Netscape
Messenger to read a newsgroup, then Web Bugs will also
work inside of HTML newsgroup messages. A Web Bug can
be used to log people who are reading messages in
particular newsgroup. Such bugs might be used for example
by investigators to track illegal activity such as
trading in child pornography and copyrighted MP3
music files. Web Bugs might also be used to monitor
people in extreme political groups.
20. Can Yahoo profiles be bugged?
Yes. For a demonstration of a bugged Yahoo profile,
This profile contains a visible Web Bug image that is being
loaded from a server other than Yahoo. The Web Bug provides
a log of everyone who has visited the profile page.