Information systems are increasingly dependent on highly distributed architectures that include multiple dependencies. Even basic attacks like script-kiddies have drastic effects on target systems as they easily spread through existing dependencies. Unless intrusion effects are accurately assessed, response systems will still be blinded when selecting optimal responses. In fact, using only response costs as a basis to select responses is still meaningless if not compared to intrusion costs. While conventional responses provoke mostly availability impacts, intrusions affect confidentiality, integrity and availability. This paper develops an approach to assess intrusion impacts on IT systems. It uses service dependencies as frames for propagating impacts. It goes beyond existing methods which mostly use dependability analysis techniques. It explores service privileges as being the main targets for attackers, and the tunable parameters for intrusion response. The approach presented in this paper is implemented as a simulation-based framework and demonstrated for the example of a vehicle reservation service.