Among the most significant features of Red Hat Enterprise Linux is SELinux (Security Enhanced Linux), a powerful, kernel-level security layer that provides fine-grained control over what users and processes may access and do on a system. By default, SELinux is enabled on Red Hat Enterprise Linux systems, enforcing a set of mandatory access controls that Red Hat calls the targeted policy. These access controls substantially enhance the security of the network services they target, but can sometimes affect the behavior of third-party applications and scripts that worked on previous versions of Red Hat Enterprise Linux.