The problem of providing cost-effective data security safeguards in personal information databanks is addressed. A structural model of databank systems is formulated, the roles of its elements in providing or threatening data privacy and security are discussed, and a suitable classification system is established. Within this framework, a model of the economic interactions of the databank protector and potential intruders is developed. The variables of this model are the value of information to the subjects--the protector and the intruders; expenditures by the protector and the intruders; and effectiveness of data security as well as intrusion techniques. Various relevant characteristics of these variables and their relationships are discussed. 36 pp. Ref.