Approaches for monitoring a host operating system. A threat model is stored and maintained in an isolated execution environment. The threat model identifies for any process executing on a host operating system how trustworthy the process should be deemed based on a pattern of observed behavior. The execution of the process and those processes in a monitoring circle relationship thereto are monitored. The monitoring circle relationship includes a parent process, any process in communication with a member of monitoring circle relationship, and any process instantiated by a present member of monitoring circle relationship. Observed process behavior is correlated with the threat model. Upon determining that a particular process has behaved in a manner inconsistent with a pattern of allowable behavior identified by the threat model for that process, a responsive action is taken.