So my Macbook pro was hacked with a RAT. I was advised to boot it with a usb containing a clean install, format the HD and reinstall. So I did. Now when I booted after a couple of days, a guest account was suddenly created and visible in the login menu. The same happened when the RAT was in there (for some reason they/he think its funny) I did not activate any guest accounts. How the heck do you get a RAT out of your system?