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Web bugs

What they are

A web bug is a hidden graphic on a Web page. Usually, they are used to log various data about the visitors of the page. Like cookies, they can be used to track your movements throughout the Web, but they are harder to spot. Technically, ad banners which are plainly visible could be called web bugs, since many use cookies to send/retrieve information to the server sending the ad. However, the term is generally used for those graphics that are designed to be as small as possible (1 pixel by 1 pixel) and clear. In other words, graphics that are deliberately hidden from the surfer. These graphics are invisible to anyone without software that detects them or without reading the source code of the web page.

Some web sites, in an attempt to hide the fact that they are web bugs, call them such things as web beacons. This is the term that Yahoo.com uses in its privacy policy.

How they are used

Advertisers may put HTML code calling a web bug alongside the URL leading to the product displayed in an ad. The web bug sends your IP address back to the advertiser, which means that this advertiser can recognize you on any site that it serves ads on. This is often used alongside cookies, or indeed may be what sets the cookie. By examining the cookie, the advertiser that set it can recognize you across any site that it has ads on.

A favored trick of spammers is to send out emails at random with the code to call a web bug from their web server. When the people who are spammed open the email, their email client will connect to the internet to download the graphic. The email address is sent to the server, which logs it. This log is used by the spammer to find active addresses to send more spam too. Never, ever open obvious spam while online, and questionable emails should be opened while offline for this very reason.

Go to this web site for a demonstration of this. Please note that we are not affiliated with the following site. Questions about this test should be directed to the webmaster and/or owners of that site.

What does a web bug look like?

They don't look like anything. That's the point.

See any graphics between these two arrows? --->  <--- There's a web bug right there; a one pixel by one pixel transparent gif graphic that's impossible to see.

Here it is again, this time with a border around it. --->  <---


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