Role based access control (RBAC) is a popular model for information security. It helps reduce the complexity of security administration and supports the review of permissions assigned to users, a feature critical to organizations that must determine their risk exposure from employee IT system access. RBAC is frequently criticized for the difficulty of setting up an initial role structure and for inflexibility in rapidly changing domains. A pure RBAC solution may have inadequate support for dynamic attributes such as time of day, which may need to be considered in determining user permissions. To support dynamic attributes, particularly in large organizations, a role explosion problem may result where thousands of separate roles are needed for different collections of permissions. Recent interest in attribute-based access control (ABAC) suggests that attributes and rules could either replace RBAC or make RBAC more simple and flexible.