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What You Need to Know About Intrusion Detection Systems

By: ProtectCyber

Posted on: 21/01/2022

The latest IBM Cost of a Data Breach report shows that the past year registered the highest data breach costs in the 17-year history of its reporting. Widely affected by remote work and compromised credentials, these costs were pegged at USD 4.24 million. This trend shows the massive impact of cyberattacks and threats to enterprises today. It also underscores the importance of having a robust cybersecurity stack. This stack includes one of the essential tools that can help boost cybersecurity—an intrusion detection system.

Here we delve into what a network intrusion detection system is, why it is essential for modern enterprises, how to choose and implement an IDS solution, and many more.

What is an intrusion detection system?

An intrusion detection system (IDS) is a monitoring system with two primary functions: anomaly detection and reporting. It can be a hardware device or software application that’s deployed on a client-server or as part of the network security of enterprise IT.

An IDS detects suspicious activities in network traffic and generates alerts to inform IT personnel of potential intrusions or malicious activities. It can identify phishing attacks, malicious software, potentially harmful traffic, and other patterns that may indicate a cyberattack. By sending timely alerts on potentially malicious activity, it helps avert furthers threat to data security.

IDS vs Firewalls

Though they are both cybersecurity solutions that are deployed to protect an endpoint, an IDS and a firewall are fundamentally different in purpose and function.

An IDS is more of a passive monitoring device that can detect potential threats and provide alerts but is unable to act on the perceived problem. It doesn’t block traffic or stop malware, and can’t provide actual protection at the endpoint or in the actual network it is deployed.

In contrast, a firewall can block known malware and perceived threats. It acts as a protective system with a boundary where certain types of traffic are prohibited from passing. Firewalls are set with predefined rules and protocols that either allow or block traffic based on network packets.

Why is an intrusion detection system important?

If an IDS doesn’t really stop malware, why do enterprises still need it?

With detecting active attacks at its very core, the functionality of an IDS is still critically important. It provides extra layers of security that can complement your firewall. It also acts as a safeguard when traditional security technologies fail.

Because an IDS detects anomalies and sends alerts instantly, IT and security personnel can pre-emptively stop cyber attackers. This mitigates potential costs in losses from full data breaches or network damage.

An IDS also helps support risk management since it is capable of identifying bugs or issues with network device or hardware configurations, minimizing potential risks.

Moreover, deploying an IDS helps with regulatory compliance by giving greater visibility across various networks. IDS logs can also be used to aid in the documentation for compliance requirements.

How does an intrusion detection system work?

An IDS is deployed at a strategic point or several within a network. It monitors network traffic to and from all devices on the network, analysing and matching them with known attacks. It scans for signatures of previously identified attacks or deviations from normal activity to detect anomalies and malicious events, such as DNS poisonings and Christmas tree scans.

Once an anomaly or deviation is detected, it is pushed up the stack and further examined at the application and protocol layer. If an attack is identified, an alert is generated and sent to the IT administrator or security operations centre analyst. The alert includes the type of attack suspected, the target address, and the source address of the intrusion. All alerts are also recorded in a central database in a security information and event management system.

Because an IDS is just a passive monitoring system, it cannot do anything further after sending an alert. There must be an incident responder tasked to act on the alert immediately. This responder must be capable of investigating issues raised by an IDS and taking appropriate actions.

Classification of Intrusion Detection Systems

IDS solutions are classified into two broad categories based on where the IDS sensors are placed, on a host or on a network.

  • Host-based IDS (HIDS)

Installed on a client computer, HIDS solutions are designed to protect a particular endpoint against both internal and external threats. A host intrusion detection system particularly monitors operating system files and has deep visibility into the internals of the host. However, its visibility is limited to its host, so it does not always offer much available context for decision-making.

  • Network-based IDS (NIDS)

NIDS are deployed on the network itself and provide visibility into all traffic flowing through that network. It can monitor the whole network and analyse incoming network traffic. This wider viewpoint enables it to provide more context for decision-making. It has a better ability to detect widespread threats and can make determinations based on packet metadata and contents. However, it offers limited visibility into the internals of host networks.

IDS Subtypes Based on Detection Method

Aside from the two broad categories according to their deployment location, IDS can be further classified into subsets based on their threat detection method and other factors. Other IDS types include signature-based IDS, anomaly-based IDS, stack-based IDS, VM-based IDS, and perimeter IDS.

  • Signature-based IDS (SIDS)

Signatures are fingerprints or patterns of known threats. These patterns include byte sequences, malicious instruction sequences, and other detected patterns identified with malware and malicious content. Signature-based IDS solutions

use these signatures to detect possible threats in traffic. While this type of IDS effectively detects previously known attacks, it is blind to zero-day vulnerabilities with no previously generated signature.

  • Anomaly-based IDS (AIDS)

An anomaly-based IDS uses newer technology that leverages machine learning to detect even previously unknown attacks. It was designed to adapt to the explosion of malware through a defined trust model that compares new behaviour with a set criterion of trustworthy activity. Statistical anomaly-based detection analyses incoming network traffic for suspected intrusion and malicious traffic. Although it can detect zero-day vulnerabilities, this type of IDS can lead to false positives where new but legitimate activities are flagged as malicious. Because it tends to mark previously unknown legitimate activity as abnormal behaviour, anomaly-based detection methods are prone to false alarms.

  • Stack-based IDS (SBIDS)

A stack-based IDS is typically used on private networks. Integrated into the TCP/IP, the SBIDS monitors data packets as they move through the entire network. When it detects a malicious packet, it pulls it out before the operating system or network applications can process it.

  • VM-based IDS (VMIDS)

As its name implies, a virtual machine-based IDS is used to monitor virtual machines and detect intrusions into a virtual network. It monitors traffic throughout all connected devices and systems.

  • Perimeter-based IDS (PIDS)

A PIDS serves as a boundary that protects the critical infrastructures of an enterprise. Placed on a specific network, it can detect suspicious activity and attempts of intrusion on a specified perimeter in a security infrastructure.


Regardless of type, IDS technology generally works the same—the system is designed to detect intrusions and alert security analysts. But with each type limited by different levels of visibility and deployment location, implementing just one specific type of IDS may not provide adequate protection. For more comprehensive security, the common practice is to use hybrid systems or to integrate multiple technologies.


Capabilities of Intrusion Detection Systems

  1. Monitoring

An IDS helps with the monitoring of firewalls, servers, routers, and existing system files needed for security controls designed for cyberattacks.

  1. Tracking

An IDS enables IT administrators to follow audit trails and logs in important operating system files that may be difficult to parse or track.

  1. Security Management

Most ISD solutions have a user-friendly interface that makes it easy for even non-technical individuals to help manage system security. While security training would be preferable, even those with very minimal knowledge can easily use an IDS dashboard.

  1. Database Building

An IDS consolidates and creates an extensive attack signature database of known threats. The system uses this database to match activities and detect malicious ones.

  1. Reporting

When malicious activity is detected, an IDS immediately generates a report and sends out alerts to notify analysts or personnel of the security breach.

Intrusion Detection System (IDS) Tools

With numerous IDS tools available today, it can be challenging to select the most ideal one for your organisation. Getting managed security services is a great option to ensure comprehensive and effective management of cybersecurity and data protection. Still, it helps to know what tools would be most useful to have in your tech stack.

SolarWinds Security Event Manager

This SEM acts as both NIDS and HIDS. It is also designed to enact both signature detection and anomaly detection for more accurate threat mitigation as it monitors network traffic. More than detection of threats, it automates responses to instances that trigger certain correlation rules. These responses include killing applications, blocking devices, changing privileges, blocking IP addresses, blocking traffic, and disabling accounts.

McAfee Network Security Platform

Not just an IDS, the McAfee NSP is an intrusion prevention system that provides real-time threat awareness and risk mitigation to physical and virtual networks. It uses both signature-based intrusion prevention and anomaly-based intrusion detection for wider visibility. Aside from unifying virtual and physical security, it is also scalable and easily integrates with other security solutions.


Combining the capabilities of a IDS, intrusion prevention systems, and network security management, Suricata can detect and avert sophisticated cyberattacks. This open-source NIDS runs on a code-based platform and is free for organisational use. Its signature-based detection approach relies on machine learning, protocol keywords, rule profiling, and pattern matching to minimise false alarms on false positives.

Selecting an IDS Solution

Although rarely used as a standalone solution, an IDS is still a valuable element for cybersecurity. It is an extra layer of protection that makes it difficult for cybercriminals to access a network undetected. Even when choosing IDS solutions to add to your cybersecurity stack, exercise due diligence and consider factors specific to your organisational needs.

First, determine what really needs protection. Assess your infrastructures and intangible assets to identify which type of IDS deployment is necessary. Consider also whether you’d need open-source IDS software or to invest in proprietary ones. Once you have a shortlist of options, check for integration capabilities with your current system and applications. You may need to get integration services for some network applications.

Consider working with a managed security service provider that can meet all your security requirements. This will ensure that an IT expert is able to respond to alerts immediately and efficiently at all times.

Final Thoughts on Intrusion Detection Systems

IDS solutions aren’t standalone, but they are still essential to any cybersecurity tech stack. As we move deeper into the digital age, intrusion detection will be even more critical to any network system. While systems are getting more advanced, so are cyber threats. To protect your business enterprise, invest in a suite of security capabilities or a security platform with intrusion detection built in.

Frequently Asked Questions

What is the purpose of an intrusion detection system?

An intrusion detection system has two main functions: detecting and reporting intrusions and potential threats. These real-time alerts enable IT and security personnel to avert further system attacks.

What are the types of intrusion detection systems?

An IDS is categorised as host-based or network-based depending on deployment location. They can further be classified into several subset types depending on how they detect intrusions. These subsets include signature-based, anomaly-based, VM-based, stack-based, and perimeter IDS.

What is the difference between an IDS and an IPS?

An IDS merely detects malicious activity in network traffic and sends alerts. It doesn’t act on the intrusion so malicious activity continues unless an IT responder acts on the alert. On the other hand, intrusion prevention systems (IPS) are capable of both detecting and responding to intrusions. They actively block a potential threat and are more effective in averting cyber threats.

About the author

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