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 at least one of the plurality of virtual networks is a virtual private network wherein the access control data comprises the following for each virtual private network: class identification (ID), private flag that indicates the class ID is private, and an availability list that lists applications that are authorized to access the virtual private network; an access control mechanism located in a system kernel of the compute node that provides data protection to nodes on the virtual private network; wherein the access control mechanism provides data protection by allowing access to authorized applications based on the access control data through a system call to the system kernel to control access to data in a memory on the plurality of compute nodes over the plurality of virtual networks, and wherein the access control mechanism further provides data protection by intercepting data access for an application that is not authorized to access data on a virtual private network based on the access control data.