"web bugs" and single-pixel GIF's

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I have heard that some people use single pixel GIF's as "web bugs or
beacons" in order to track page accesses.  I am new at web design; could
someone please explain how this would be done?



Re: "web bugs" and single-pixel GIF's

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One way is to use an image such as:
<img src="/track.asp?pageId=42" alt="" width="1" height="1" />

Where "track.asp" is a script executed on the webserver that returns the
transparent gif (etc) image to the client. The information on the
querystring is the tracking information that has a relationship with the
webpage being viewed. This is likely processed and stored in a database
in some way for whatever reason, usually alongside cookie information so
that a users behaviour can be tracked and site navigation patterns

Fortunately some browsers and third-party devices filter out such
markup. This is just as well because HTML email spammers often use this
trick to register your email address as valid and active so that they
may sell your email address to someone else for increased profit. In
such cases the querystring information is an identifier unique to your
email address.

Thus, the simple act of viewing such a spam HTML email in a browser
without a filtering mechanism or a browser derivative (Outlook Express)
will submit valuable information to unknown third parties without your
consent. The technique can be applied to almost any externally
referenced object in a page (any image, css file, javascript file,
object, etc.) ergo I doubt that web-bug filters are clever enough to
catch all forms of this practice. You're safer with plain text, assuming
you don't follow "Click here to unsubscribe" links...
Andrew Urquhart
Reply: www.andrewu.co.uk/about/contact/?subject=Re%3A+alt.html

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