Applicability detection using third party target state

Aspects of the subject matter described herein relate to detecting needed updates. In aspects, an update agent receives a request to scan for updates for a target. The target may include a virtual or non-virtual device. The request may include one or more rules that indicate resources to check to determine attributes of the device. The update agent utilizes a resource accessor to access the resources indicated by the rules. The resource accessor maps resource names indicated by the update agent to corresponding resource names of the target. The update agent may provide results of evaluating the rules to an update source in a multi-pass protocol designed to eliminate irrelevant updates.