ELSEC 2.5 is a security hardening tool for Linux operating systems. It is a set of scripts that make the configuration of Linux operating systems more secure by performing various security-related tasks, such as tightening system requirements, applying security patches, and enforcing access control. It also provides additional features like log monitoring and intrusion detection. It is compatible with most popular Linux distributions and can be used to harden servers, desktops, and even embedded devices.