• save the configuration.php file and your images and personal files one by one, (not the folder as it may contain unwanted files)
  • wipe the entire folder where Joomla! is installed
  • upload a new clean full package latest version of joomla 1.5.x or Joomla 2.5.x (minus the install folder)
  • reupload your configuration file & images.
  • reupload or reinstall the latest versions of your extensions , templates (even better is to use original clean copies to ensure that the hacker/defacer did not leave any shell script files in your site)

To do this will take your site off line for around 15 minutes. To track down your hacked/defaced html may take hours or even longer.