So you openly admit the machine IS NOT YOURS. You are essentially keeping them from their own machine, which I find unethical. I can't blame them for taking matters into their own hand and rebooting the system into single-user mode and locking you out until you play nice.
Stop being a jerk and cooperate with the owners of the machine you are renting or take your data elsewhere.
Simply because they own the property does not give them the right to invade your privacy. There is still the illusion of privacy here, right?