The intrusion detection system. This system is often combined with an IPS. This way you are even more protected to malicious activity on your network.
What does an IDS
It sees malicious activity in your network. In this way the system scans your network. And sees which information can go through and which information cannot go through. You could call the intrusion detection system, the private detective of your network.
Where do you need it for?
Modern network connections, need a higher security level than ten years ago. So nothing could happen, with your personal data. But before you can stop the problem, you have to see it. This is where the Intrusion detection system is helping you, to stop the problem you can use an IPS.