ModSecurity is a plugin for Apache web servers which functions as a web application layer firewall. It is employed to prevent attacks towards script-driven websites by employing security rules which contain particular expressions. This way, the firewall can stop hacking and spamming attempts and preserve even websites that are not updated often. For instance, multiple unsuccessful login attempts to a script admin area or attempts to execute a certain file with the purpose to get access to the script shall trigger specific rules, so ModSecurity will block these activities the moment it identifies them. The firewall is incredibly efficient because it tracks the entire HTTP traffic to a website in real time without slowing it down, so it can stop an attack before any harm is done. It additionally keeps an incredibly thorough log of all attack attempts which includes more info than conventional Apache logs, so you could later analyze the data and take further measures to increase the security of your sites if needed.