ModSecurity is a plugin for Apache web servers that functions as a web app layer firewall. It is used to stop attacks against script-driven sites by employing security rules which contain certain expressions. In this way, the firewall can prevent hacking and spamming attempts and shield even sites which are not updated frequently. For example, numerous unsuccessful login attempts to a script admin area or attempts to execute a particular file with the intention to get access to the script shall trigger certain rules, so ModSecurity will block out these activities the moment it discovers them. The firewall is very efficient as it screens the entire HTTP traffic to a website in real time without slowing it down, so it can easily prevent an attack before any damage is done. It also maintains an incredibly thorough log of all attack attempts which includes more information than traditional Apache logs, so you could later check out the data and take additional measures to enhance the security of your websites if required.