favicon.ico is an icon file Internet Explorer 5 looks for when someone using IE bookmarks your website. If favicon.ico exists and is in the right format, IE will download that image and use it in your favorites list, location bar and desktop. If favicon.ico doesn't exist, then you get a "File does not exist" error in your error log.

The easiest way to make a valid favicon.ico is to use the online java favicon.ico generator at http://www.favicon.com

Poor, poor Microsoft. I'm not surprised to hear that they have once again opened another privacy hole without even realizing it. If one were particularly fiendishly evil, they could symlink this to a CGI script that dumps all sorts of information about the unsuspecting user. The perfect marketing tool, they would now have a list of people interested enough to bookmark it, and perhaps even their login, IP address, et cetera.

Well, even then, it would be quite limited in its badassery, in that you can't dump much from a single script. But combined with cookies, then, oh, boy.

These icons also work in Konqueror, as well as the most recent Mozilla builds.

Although "favicon.ico" is the default filename for these icons, it is possible to use other files. Doing so, however, requires the use of a LINK tag in the page's header. The format is:

<link rel="Shortcut Icon" href="URL-of-icon" />

Also note that Mozilla can use any image format it supports as a favicon; it isn't limited to the fairly obscure .ico format.

As a side benefit: Many Webmasters complain about having their logs spammed with errors when browsers ask for favicons that don't exist. By putting up a favicon, you can help keep your logs cleaner.

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