ACF2 (more formally, CA-ACF2; the ACF stands for Access Control Facility) is a set of programs from Computer Associates that enable security on mainframes. ACF2 prevents accidental or deliberate modification, corruption, mutilation, deletion, or viral infection of files. With ACF2, access to a system is denied to unauthorized personnel. Any authorized or unauthorized attempt to gain access is logged. System status can be monitored on a continuous basis, and a permanent usage log can be created. The logging feature, besides helping to identify potential intruders, makes it possible to identify and analyze changes and trends in the use of the system. Settings can be changed on a moment's notice, according to current or anticipated changes in the security or business requirements of the organization using the system.