Security
• Some users or applications on a system may be less than completely trustworthy and therefore the operating system needs to limit the scope of what they can do. • Without protection, a malicious user might change application files or even the operating system itself. – For example, if a malicious application is permitted to write directly to the disk, it could modify the file containing the operating system’s code, so that the next time the system starts, the modified operating system will boot instead, installing spyware and disabling virus protection. For security, an operating system must prevent untrusted code from modifying system state.