@geniee
You have turn on SmartScreen. You can turn it off or you or in contrary you need to allow FRST to be run by clicking Run anyway in SS pop-up.:

  • Wen you run FRST/FRST64, click on Run anyway (again Run button on UAC screen) and tool should start.
    or…
  • Disable SmartScreen by clicking flag in system tray > Action Center > Change Windows SmartScreen settings > Don’t do anything (turn off…) > Ok

    http://fotkica.com/thumbs3/1_tmb_92721660_W8_SS.jpg