After an audit, an administrator discovers all users have access to confidential data on a file server. Which of the following should the administrator use to restrict access to the data quickly?

Access control lists (ACLs) are the most direct and efficient method to restrict access to specific data on a file server. An ACL defines permissions for users and groups to access objects like files and folders. By modifying the ACLs on the confidential data, the administrator can immediately revoke unauthorized users' access and grant it only to approved personnel. Group Policy is used for managing user and computer settings across a network, but it doesn't directly control file-level access permissions as granularly or immediately as ACLs for existing data. Content filtering inspects data for specific content and is used more for network traffic or email, not for restricting access to stored files. Data loss prevention (DLP) systems monitor and prevent sensitive data from leaving an organization's control, but they don't primarily function to restrict internal access to files on a server.