To control privileges and access to resources on a per-process basis, an administrator creates a rule that may be applied to modify a process's token. The rule includes an application-criterion set and changes to be made to the groups and/or privileges of a token. The rule is set as a policy within a group policy object (GPO), where a GPO is associated with one or more groups of computers. When a GPO containing a rule is applied to a computer, a driver installed on the computer accesses the rule(s) anytime a logged-on user executes a process. If the executed process satisfies the criterion set of a rule the changes contained within the rule are made to the process token, and the user has expanded and/or contracted access and/or privileges for only that process.