Angry IP Scanner primarily functions as an active scanner tool that sends packets to various hosts and analyzes responses to gather information about them; however, stating it's incapable of passive scanning is incorrect because, through plugins or integration with other tools, passive scanning functionalities can be extended to it. Active scanning refers to the tool's ability to send packets to systems on the network to solicit responses, whereas passive scanning typically involves analyzing network traffic without sending probe requests, which is not a direct feature of Angry IP Scanner. Nevertheless, by integrating Angry IP Scanner with other tools or through certain configurations, one could indirectly perform passive observations.