Understanding the 5 Types of Intrusion Detection Systems

As the number of cyberattacks and intrusions continue to rise, monitoring and securing your company’s network has never been more pressing. 

In 2021 alone, the FBI’s Internet Crime Complaint Center (IC3) received more than 800,000 complaints about data breaches, malware and more. These complaints totaled nearly $7 billion in losses—and they only represent the reported cases.

If you want to protect yourself and your business from these threats, you need a comprehensive cybersecurity setup. One vital piece of the puzzle is an Intrusion Detection System.

An Intrusion Detection System (IDS) plays the role of a scout or security guard in your network, watching for suspicious attempts and notifying you as needed. However, there are several kinds of IDS solutions on the market today.

With that in mind, we’ll look at the five different types of intrusion detection systems, as well as the detection methods they use to keep your network safe.

What is an Intrusion Detection System?

An Intrusion Detection System (IDS) is a technology solution that monitors inbound and outbound traffic in your network for suspicious activity and policy breaches. As the name suggests, the primary purpose of an IDS is to detect and prevent intrusions within your IT infrastructure, then alert the relevant people. These solutions can be either hardware devices or software applications.

Typically, an IDS will be part of a larger Security Information and Event Management (SIEM) system. When implemented as part of a holistic system, your IDS is your first line of defense. It works to proactively detect unusual behavior and cut down your mean time to detect (MTTD). Ultimately, the earlier you recognize an attempted or successful intrusion, the sooner you can take action and secure your network.

It’s worth noting that most (but not all) IDSs are solely passive. In other words, they don’t actually protect your systems and networks from malicious activity. However, they do give you the information you need to keep your systems safe. And when it comes to cybersecurity, that kind of information is everything.

5 Different Types of Intrusion Detection Systems

Although all intrusion detection systems fulfill the same purpose, they work in slightly different ways. Altogether, there are five IDS types. Let’s explore the details, advantages, and drawbacks of each one.

1. Network Intrusion Detection System

A Network Intrusion Detection System (NIDS) is a solution that monitors your entire network through one or more touchpoints. To use a NIDS, you generally need to install it on a piece of hardware within your network infrastructure. Once installed, your NIDS will sample every packet (a collection of data) that passes through it.

Your typical NIDS can examine all the traffic that goes through it. With that said, you may not want to analyze everything that comes through your NIDS, as you could end up missing an intrusion attempt due to information overload.

To combat this issue, most NIDSs allow you to create a set of “rules” that define the type of packets your NIDS will pick up and store. Rules let you hone in on certain types of traffic, but they also require some knowledge of the NIDS’ syntax.

NIDSs are beneficial because:

  • They can analyze all inbound and outbound traffic
  • They detect events in real-time, allowing for quick response times
  • They’re more challenging for intruders to detect
  • They can be strategically placed in critical areas

However, NIDSs aren’t perfect. Potential downsides include:

  • Hands-on maintenance – Because a NIDS is typically installed on a dedicated piece of hardware, you may need to spend more time manually interacting with it.
  • Low specificity – The more traffic a NIDS tool analyzes, the more likely it is to lack specificity and miss signs of an intrusion.

2. Network Node Intrusion Detection System

A Network Node Intrusion Detection System (NNIDS) is technically a variation of a NIDS, but since it works differently, we’ll consider it a different type of IDS.

A NNIDS also analyzes the packets that pass through it. However, instead of relying on a central device to monitor all network traffic, the system watches over each node connected to your network.

This differentiation comes with several benefits, such as:

  • Higher speeds – Since the amount of traffic each NNIDS agent analyzes is reduced, the system can work faster.
  • Taking up fewer resources – In the same vein, NNIDS uses fewer system resources. As such, you can easily install it on your current servers.

The main drawback of opting for a NNIDS is the need for multiple installations. While a NIDS only requires one device, NNIDS needs several—one for every server you want to monitor. Additionally, all of these NNIDS agents need to report to a central dashboard.

3. Host Intrusion Detection System

A Host Intrusion Detection System (HIDS) takes the device independence of NNIDS one step further. With a HIDS, you can install IDS software on every device connected to your network.

HIDSs work by taking “snapshots” of their assigned device. By comparing the most recent snapshot to past records, the HIDS can identify the differences that could indicate an intrusion.

HIDSs are advantageous because:

  • They can be installed on computers or servers
  • They can pinpoint the affected device
  • They notify administrators if analytical system files were modified or deleted
  • They’re particularly effective against insider threats

Unfortunately, HIDS solutions can suffer from “after-the-fact” monitoring. Because many HIDS solutions rely on logs that record intrusions, your mean time to respond (MTTR) may be slower overall. As such, proper use of an HIDS requires frequent monitoring.

4. Protocol-Based Intrusion Detection System

A Protocol-Based Intrusion Detection System (PIDS) is a specific IDS that monitors the protocol in use. In practice, this system typically analyzes the HTTP or HTTPS protocol stream between your devices and the server.

In most cases, a PIDS will go at the front end of a server. The system can protect your web server by monitoring inbound and outbound traffic.

Because they focus on the protocol (the way devices transmit information within a network), PIDSs aren’t necessarily a comprehensive IDS solution. However, they can augment an already robust cybersecurity solution.

5. Application Protocol-Based Intrusion Detection System

An Application Protocol-Based Intrusion Detection System (APIDS) is a type of IDS that specializes in software app security. Typically associated with host-based intrusion detection systems (HIDS), APIDSs monitor the communications that occur between applications and the server. An APIDS is typically installed on groups of servers.

As with a PIDS, an APIDS is unlikely to solve all of your network monitoring needs. Still, it can complement other types of IDS.

The 3 Intrusion Detection System Methods

Depending on the type of intrusion detection system you choose, your security solution will rely on a few different detection methods to keep you safe. Here’s a brief rundown of each one.

1. Signature-Based Intrusion Detection

Signature-Based Intrusion Detection Systems (SIDS) aim to identify patterns and match them with known signs of intrusions. 

A SIDS relies on a database of previous intrusions. If activity within your network matches the “signature” of an attack or breach from the database, the detection system notifies your administrator.

Since the database is the backbone of a SIDS solution, frequent database updates are essential, as SIDS can only identify attacks it recognizes. As a result, if your organization becomes the target of a never before seen intrusion technique, no amount of database updates will protect you.

2. Anomaly-Based Intrusion Detection

On the other hand, an Anomaly-Based Intrusion Detection System (AIDS) can identify these new zero-day intrusions.

An SIDS uses machine learning (ML) and statistical data to create a model of “normal” behavior. Anytime traffic deviates from this typical behavior, the system flags it as suspicious.

The primary issue with AIDS vs. SIDS is the potential for false positives. After all, not all changes are the result of malicious activity; some are simply indications of changes in organizational behavior. But because a SIDS has no database of known attacks to reference, it may report any and all anomalies as intrusions. 

3. Hybrid Intrusion Detection

A hybrid system combines the best of both worlds. By looking at patterns and one-off events, a Hybrid Intrusion Detection system can flag new and existing intrusion strategies.

The only downside to a hybrid system is the even bigger uptick in flagged issues. However, considering that the purpose of an IDS is to flag potential intrusions, it’s hard to see this increase in flags as a negative.

Helixstorm: Managed IT Security for Your Business

By now, you’ve probably realized that every cybersecurity solution has its pros and cons, and no two businesses will need the same setup. In fact, in most cases, a multilayered approach works best. When you combine more than one type of IDS, you can protect your network from every angle.

At Helixstorm, we can help you decide on the best intrusion detection system (or systems) for your business needs. And our managed security services don’t stop there; our experts will continue to monitor and maintain your IDS alongside the rest of your cybersecurity systems.

Get in touch with us today to learn more about our business-first philosophy that protects your entire enterprise.


Internet Crime Complaint Center. Internet Crime Report 2021. https://www.ic3.gov/Media/PDF/AnnualReport/2021_IC3Report.pdf

SpringerOpen. A critical review of intrusion detection systems in the internet of things: techniques, deployment strategy, validation strategy, attacks, public datasets and challenges. https://cybersecurity.springeropen.com/articles/10.1186/s42400-021-00077-7