def _disable_check(check, elem)
      checks = REXML::XPath.first(@xml, '//VulnerabilityChecks')
      checks.elements.delete("Enabled/#{elem}[@name='#{check}']")
      disabled_checks = checks.elements['Disabled'] || checks.add_element('Disabled')
      disabled_checks.add_element(elem, { 'name' => check })