ModSecurity is a plugin for Apache web servers which functions as a web application layer firewall. It's used to stop attacks toward script-driven Internet sites through the use of security rules that contain specific expressions. This way, the firewall can block hacking and spamming attempts and preserve even sites which aren't updated regularly. For example, a number of unsuccessful login attempts to a script administrative area or attempts to execute a certain file with the intention to get access to the script shall trigger certain rules, so ModSecurity shall block these activities the minute it discovers them. The firewall is quite efficient because it screens the entire HTTP traffic to a website in real time without slowing it down, so it could stop an attack before any harm is done. It also maintains an exceptionally thorough log of all attack attempts that contains more information than conventional Apache logs, so you could later check out the data and take extra measures to enhance the security of your Internet sites if required.