An intrusion prevention system (**IPS**) is an application that monitors system activity for intrusive activity and takes action to stop the activity. An IPS works similarly to an [[Intrusion Detection System|IDS]]. But, IPS monitors system activity to detect and alert on intrusions, and it also *take action to prevent the activity and minimise its effects*. For example, an IPS can send an alert and modify an access control list on a router to block specific traffic on a server.