ModSecurity is a plugin for Apache web servers which acts as a web application layer firewall. It's employed to prevent attacks towards script-driven websites through the use of security rules that contain specific expressions. In this way, the firewall can stop hacking and spamming attempts and preserve even sites which aren't updated on a regular basis. For instance, multiple unsuccessful login attempts to a script administrator area or attempts to execute a specific file with the purpose to get access to the script shall trigger particular rules, so ModSecurity shall stop these activities the minute it detects them. The firewall is incredibly efficient since it tracks the entire HTTP traffic to a site in real time without slowing it down, so it can easily stop an attack before any damage is done. It also keeps a very comprehensive log of all attack attempts which contains more information than typical Apache logs, so you can later check out the data and take extra measures to increase the security of your Internet sites if required.