How does intrusion detection software fit into a computer security plan?

It monitors network ports and application activity, and reports suspect activity to the system administrators and/or system logs. The most advanced IDS packages can detect internal and external intrusions (those that occur inside and outside the firewall, respectively), on any port, to any application. They are also programmed to watch for unusual activity, such as a large spike of bandwidth that would threaten to overwhelm the application or hardware.