A DoS vulnerability of Apache HTTPD Web Server is found. It lies on the way the web server handles multiple overlapping ranges. It affects all version of 1.3 and 2 of Apache Web Server. If you have installed Apache server with the default settings then you are vulnerable. Apache Software Foundation is working on this issue and they will release a fix soon, but until then they offer some immediate actions you can do to be protected. These actions are explained in the link provided at the beginning of this post.
There are already some tools that exploit that vulnerability and several attacks took place. One of them is Killapache, a Perl script posted here which demonstrates the problem. With such tools, you can cripple a web server from a single PC.