ModSecurity is a plugin for Apache web servers that acts as a web application layer firewall. It is employed to stop attacks toward script-driven websites through the use of security rules that contain specific expressions. That way, the firewall can prevent hacking and spamming attempts and shield even websites which are not updated on a regular basis. As an example, several failed login attempts to a script administrator area or attempts to execute a particular file with the intention to get access to the script will trigger specific rules, so ModSecurity will stop these activities the instant it discovers them. The firewall is quite efficient as it screens the whole HTTP traffic to a website in real time without slowing it down, so it could stop an attack before any damage is done. It additionally keeps a very detailed log of all attack attempts which features more information than standard Apache logs, so you could later analyze the data and take additional measures to increase the security of your websites if needed.