1. A multi-node computer system comprising: a plurality of compute nodes that each comprise a processor and memory connected by a plurality of virtual networks; an access setup mechanism that configures access control data on the compute nodes to indicate a security class associated with a virtual network and one or more users on the multi-node computer system, and where the access control data further includes a security class attribute associated with database objects in the memory; and an access control mechanism that controls access to the database objects over the virtual network by sending a query to a particular security class so the query is only seen by those nodes that are authorized by the equivalent security class indicated in the access control data.