Are you certain? This must be new, because before your would get a fresh machine every time. Anytime you boot, AMZ looks at the image you want to run, and they unpack and uninstall it for you, meaning that even a reboot led to a clean drive. Now, there's been some talk about 'shadow copies' where you might even get access to other customers data by simply starting a deep scan on the drive.. but that's hardly persistence.