ModSecurity is a plugin for Apache web servers which functions as a web app layer firewall. It is employed to stop attacks against script-driven Internet sites by using security rules which contain particular expressions. That way, the firewall can prevent hacking and spamming attempts and preserve even sites that aren't updated regularly. As an example, several unsuccessful 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 specific rules, so ModSecurity shall stop these activities the instant it identifies them. The firewall is quite efficient as it screens the whole HTTP traffic to an Internet site in real time without slowing it down, so it can prevent an attack before any damage is done. It furthermore maintains an incredibly comprehensive 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 enhance the security of your sites if necessary.