Root privilege

This is a seperate entry because -- surprise -- you don't have to be root to run programs (or for daemons to run themselves) as root in order to have root privilege. Any daemon, user or group that has a uid or gid of 0 runs as root effectively. So anyone that hijacks an account that has a root uid is effectively root. Which is why it's a good idea to run as few programs as possible that do that.