Traditional network security technologies such as firewalls and intrusion detection systems usually work according to a static ruleset only. We believe that a better approach to network security can be achieved if we use quantified levels of risk as an input. In this paper, we describe a dynamic access control architecture which uses risk to determine whether to allow or deny access by a source connection into the network. A simulation of our architecture shows favorable and promising results. Categories and Subject Descriptors C.2.0 [Computer-Communication Networks]: General— security and protection; C.2.3 [Computer-Communication Networks]: Network Operations—network management, network monitoring; K.6.5 [Management of Computing and Information Systems]: Security and Protection— authentication, invasive software, unauthorized access General Terms Security, management, algorithms Keywords Dynamic access control, network management, risk, risk awareness, role