The disclosure herein provides data security on a parallel computer system using virtual private networks connecting the nodes of the system. A mechanism sets up access control data in the nodes that describes a number of security classes. Each security class is associated with a virtual network. Each user on the system is associated with one of the security classes. Each database object to be protected is given an attribute of a security class. Database objects are loaded into the system nodes that match the security class of the database object. When a query executes on the system, the query is sent to a particular class or set of classes such that the query is only seen by those nodes that are authorized by the equivalent security class. In this way, the network is used to isolate data from users that do not have proper authorization to access the data.