This document describes tools capable of making a portion of operating-system memory associated with a protection agent unalterable or inaccessible from an operating-system privilege mode. In some embodiments, these tools are capable of creating a protection-agent privilege mode by requesting that a virtual machine monitor protect this portion of operating-system memory. In other embodiments, these tools are capable of creating the protection-agent privilege mode by virtualizing a physical processor into multiple virtual processors, at least one of which is a protection-agent virtual processor designed to run the protection agent. By making this portion of operating-system memory unalterable or inaccessible from the operating-system privilege mode, the protection agent may be less vulnerable to attacks by entities operating within the operating-system privilege mode.