There is a bug in certain versions of Apache that is susceptible to a dDoS using malformed GET requests. You can find more information about “killapache” at the following site.

http://www.pentestit.com/2011/08/25/killapache-ddos-tool-freezes-apache-web-server/

There is no patch, however their is a work around for this bug which is provided below. In Ubuntu or Debian create a new file “/etc/apache2/conf.d/killapache-fix” and place the following code

You may need to install the “headers” module, which can be done by typing “a2enmod headers” and then you should be able to reload apache without errors.