Security trimming is a feature which allows you to hide the urls based on the roles. This mean you can have a single web.sitemap file which contains all the urls of the website. The urls will be served to the users based on the roles. A common place where security trimming is used is when you want to display a menu based on the user role. To get started with sitemap and security trimming check out the following post:
http://geekswithblogs.net/azamsharp/archive/2006/05/02/77018.aspx
Now, sometimes we need to display absolute urls like http://www.gridviewguy.com or www.koffeekoder.com. If security trimming is enabled you won't be able to see these urls even when you are authenticated. The solution is very simple. Place the '*' as a value for the roles attribute in web.sitemap file as shown below:
<siteMapNode url="~/" title="" description="">
<siteMapNode url="~/Default.aspx" title="Home" description="" />
<siteMapNode url="~/Members/Add.aspx" title="Add" description="" roles="Member" />
<siteMapNode url="http://www.yahoo.com" title="yahoo" roles="*" />
</siteMapNode>
roles="*' means that the siteMapNode is visible to everyone.