Systems, methods, and interfaces for the management of virtual machine networks and other programmatically controlled networks are provided. Hosted virtual networks are configured in a manner such that a virtual machine manager of the virtual network may monitor activity such as user requests, network traffic, and the status and execution of various virtual machine instances to determine possible security assessments. A security assessment may be performed before, after, or simultaneous to the execution of the activity associated with the security assessment event. The execution of an activity may further be synchronous with the results of the security assessment. The timing of the assessment may correspond to the type of assessment or type of activity that is requested or detected.