Just to be clear, and because there seems to be a lot of confusion on this, you are not actually flashing (writing) Flashcast to your Chromecast. Flashcast is a software tool that resides on the USB flash drive to which you write it. The first time you plug that drive into your Chromecast Flashcast will run and properly setup its FAT32 working space on your USB flash drive. Nothing is flashed to your Chromecast at this point, and your Chromecast is still running whatever it was so is not rooted or update safe! When you then remove the USB flash drive and plug it into your computer to copy eureka_image.zip (e.g. the rooted, non-updating firmware) to it, you are copying it to the working space that Flashcast set up on first run. It is only when you then plug Flashcast into your Chromecast again that Flashcast flashes (writes) the eureka_image.zip to your Chromecast.