ModSecurity is a plugin for Apache web servers that functions as a web app layer firewall. It is used to stop attacks towards script-driven Internet sites through the use of security rules which contain specific expressions. This way, the firewall can stop hacking and spamming attempts and preserve even sites that aren't updated on a regular basis. For instance, numerous failed login attempts to a script administrative area or attempts to execute a specific file with the objective to get access to the script will trigger certain rules, so ModSecurity shall stop these activities the minute it detects them. The firewall is quite efficient since it monitors the entire HTTP traffic to a site in real time without slowing it down, so it can easily prevent an attack before any harm is done. It furthermore keeps an incredibly thorough log of all attack attempts which features more info than typical Apache logs, so you can later examine the data and take additional measures to improve the security of your sites if required.