Abstract : We examine the concept of security as a dimension of Quality of Service in distributed systems. Implicit to the concept of Quality of Service is the notion of choice or variation. Security services also offer a range of choice both from the user perspective and among the underlying resources. We provide a discussion and examples of user-specified security variables and show how the range of service levels associated with these variables can support the provision of Quality of Security Service, whereby security is a constructive network management tool rather than a performance obstacle. We also discuss various design implications regarding security ranges provided in a QoS-aware distributed system.