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What is an Intrusion Detection System (IDS)?

Read our guide on intrusion detection systems to find out what they are, why they’re important, challenges & considerations & lots more.

intrusion detection system

If there’s an intruder in your network or a breach in your security policy, who will be the one to sound the alarm? You need a carefully positioned whistleblower in your first line of defense. You need an Intrusion Detection System. It’s an essential component of any comprehensive cybersecurity strategy. But why is this tool so crucial? You’ll learn all about it in our latest blog.

This guide will cover: 

  • What are intrusion detection systems? 
  • Types of intrusion detection systems 
  • How do intrusion detection systems work? 
  • What is an example of an intrusion detection system? 
  • Why are intrusion detection systems important?
  • Challenges of intrusion detection systems
  • IDS evasion techniques
  • Things to consider when choosing an IDS 
  • IDS implementation best practices 
  • FAQs 

What are intrusion detection systems?

Intrusion Detection Systems (IDS) are security technologies designed to detect and respond to unauthorized or suspicious activities within computer networks, systems, and applications. Their primary function is to monitor network traffic, analyze data packets, and identify potential security breaches or intrusion attempts.

At its core, an IDS will identify two main types of activities: malicious attacks and policy violations. Malicious attacks involve deliberate attempts to exploit vulnerabilities or gain unauthorized access to systems, while policy violations refer to activities that violate predefined security policies or acceptable usage guidelines.

Types of intrusion detection systems

Overall, an IDS can be classified into two main categories, let’s explore them in greater detail. 

Network-Based IDS (NIDS)

NIDS are deployed at specific points within a network infrastructure, typically at network gateways or within segments. They analyze network traffic in real-time, monitoring packets as they traverse the network.

NIDS use various techniques, such as signature-based detection, anomaly-based detection, or behavior-based detection, to identify suspicious patterns or known attack signatures.

When a potential intrusion is detected, NIDS generate alerts that can be further analyzed or trigger immediate response actions.

Host-Based IDS (HIDS)

HIDS reside on individual hosts or servers, monitoring activity occurring on the specific system where they are installed.

Unlike NIDS, HIDS focus on the activities and behaviors of the host itself, rather than analyzing network traffic. HIDS monitors system logs, file integrity, registry changes, and other host-specific events to identify potential intrusions or policy violations.

It provides granular visibility into individual systems and can detect both internal and external threats that may not be captured by network-based monitoring alone.

Other types of IDSs

Within NIDS and HIDS, you can also find a range of intrusion detection systems that have different deployment, detection methods, and functionality. For example: 

  • Signature-based IDS: these IDS use pre-defined signatures or patterns of known attacks to identify and alert on malicious activities. They are effective at detecting well-known threats but may struggle with detecting new or unknown attacks.
  • Anomaly-based IDS: this type of IDS establishes a baseline of normal behavior for the network or host and raises alerts when it detects deviations from that baseline, which may indicate potential intrusions.
  • Heuristic-based IDS: heuristic IDS use rules and patterns to identify potential threats. They look for deviations from established norms or attack patterns.
  • Behavior-based IDS: behavior-based IDS focus on analyzing the behavior of users, applications, or systems to detect anomalies and signs of potential threats.
  • Hybrid IDS: hybrid IDS combines multiple detection methods, such as signature-based and anomaly-based approaches, to enhance the accuracy and effectiveness of intrusion detection. 

How do intrusion detection systems work?

Intrusion detection systems monitor network traffic, system logs, and other relevant data sources to detect and respond to potential security breaches. Here’s a general overview of how an IDS works:

  1. Data collection: IDS collect data from multiple sources, such as network packets (NIDS) or host activities (HIDS) to monitor events like network traffic, system logs, event logs, file integrity information, registry changes, and more.
  2. Traffic analysis: in the case of NIDS, the captured network traffic is analyzed in real-time or offline. It looks for suspicious patterns, using signature-based, anomaly-based, or behavior-based techniques.
  3. Alert generation: when an IDS detects a potential intrusion or suspicious activity, it generates alerts. These alerts can be in the form of log entries, email notifications, or integration with a Security Information and Event Management (SIEM) system.
  4. Incident response: security teams analyze the data, assess the impact, and implement necessary measures to contain and remediate security incidents effectively.
  5. Continuous monitoring and updates: IDSs need to adapt to new attack techniques and evolving threats. This involves updating the IDS software, attack signature databases, and monitoring the latest vulnerabilities and attack methods.

What is an example of an intrusion detection system?

Snort is a popular open-source network-based intrusion detection system developed by Sourcefire (now owned by Cisco). It combines signature-based detection and anomaly-based detection to identify and respond to potential intrusions.

Snort operates by analyzing network traffic and comparing it against a set of predefined rules or signatures. Any potential intrusions detected within traffic that matches these rules will generate an alert accordingly. Snort offers flexibility by allowing users to create custom rules and modify existing ones to suit their specific needs. 

In addition to its detection capabilities, Snort can respond to detected threats by generating alerts, logging events, or blocking traffic in real-time, making it an intrusion prevention system (IPS) as well. It also features a large user community, and its open-source nature encourages collaboration, rule sharing, and ongoing development. 

Why are intrusion detection systems important?

Intrusion Detection Systems play a vital role in ensuring the security and integrity of computer networks and systems. Here’s why IDSs are important:

Early threat detection

IDS continuously monitors network traffic, logs, and data sources to detect intrusions in real-time, enabling prompt incident response and minimizing potential damage. Early detection helps organizations mitigate threats and reduce the chances of successful attacks.

Proactive defense

IDS offer proactive defense against malicious activities and unauthorized access attempts. They identify and block network-based attacks like port scans and DoS attacks, safeguarding digital assets’ availability, confidentiality, and integrity. 

Insider threat detection

IDS can identify suspicious activities initiated by authorized users or insiders with malicious intent. Behavior-based IDS, in particular, can detect anomalies in user behavior, such as unauthorized privilege escalation, data exfiltration, or unauthorized access attempts to sensitive information.

Compliance and regulatory requirements

IDS helps organizations meet compliance regulations by offering continuous monitoring, event logging, and audit trail generation. Demonstrating compliance helps prevent penalties, legal consequences, and reputational harm, ensuring adherence to industry regulations.

Incident response and forensics

IDS generates alerts for incident response and forensic investigations. Security teams analyze and investigate alerts to mitigate the impact of intrusions. IDS logs and data serve as valuable evidence during forensic investigations, aiding in understanding the breach’s nature, identifying its scope, and facilitating the recovery process.

Enhanced security posture

Integrating IDS with other security controls, like firewalls, antivirus software, and SIEM systems, creates a comprehensive security posture. IDS also enhances threat detection capabilities, providing added visibility into network and system activities, resulting in more effective incident response.

Ongoing threat intelligence

IDS benefit from continuous updates and threat intelligence feeds, staying informed about new attack methods and vulnerabilities. This adaptability enables IDS to provide the latest defenses against potential intrusions, keeping organizations protected from evolving threats.

Challenges of intrusion detection systems

While intrusion detection systems are valuable tools in cybersecurity, they also face certain challenges, such as:

  • False positives and negatives: IDS can produce false alerts, flagging legitimate activities as potential threats, or miss actual intrusions, demanding careful tuning and continuous improvement of detection rules.
  • Evasion techniques: hackers use sophisticated methods to avoid IDS detection, like encryption and low-and-slow attack patterns, requiring IDS to keep up with evolving threats.
  • Network complexity: complex networks strain IDS performance, necessitating scalability and optimization for effective monitoring.
  • Zero-day exploits: signature-based IDS may miss unknown threats, highlighting the need for anomaly and behavior-based detection methods.
  • Resource demands: IDS can be computationally intensive, requiring adequate hardware and resources for optimal performance.
  • Response and remediation: Efficient response to IDS alerts requires skilled personnel, well-defined incident response processes, and integration with security workflows.

IDS evasion techniques

Cybercriminals actively try to evade IDSs and other security measures. Here are some common techniques they can employ: 

  1. Encryption: by encrypting their communication, attackers can hide the contents of network packets from IDS, making it challenging to detect any malicious payloads or commands.
  2. Polymorphic malware: polymorphic malware is designed to continuously change its code or behavior, making it difficult for signature-based IDS to identify the malicious software based on predefined signatures.
  3. Fragmentation: cybercriminals may fragment network packets to distribute malicious payloads across multiple packets, helping bypass signature-based IDSs.
  4. Traffic manipulation: attackers can use packet-level techniques like source IP address spoofing or fragmenting packets in specific ways to evade detection.
  5. Covert channels: cybercriminals transmit data or commands through alternative communication paths that are unmonitored by IDS.
  6. Polymorphic shellcode: shellcode employs techniques like code obfuscation, or encryption making it difficult for IDS to recognize and detect malicious code within network traffic.
  7. Timing and traffic patterns: by aligning their activities with regular traffic patterns or specific periods of network congestion, cybercriminals evade anomaly-based IDS. 

Things to consider when choosing an IDS

When choosing an IDS, several factors should be considered to ensure it meets your specific needs and provides effective protection for your network and systems. For example:

  • Deployment: choose NIDS or HIDS based on your network’s needs, considering where the IDS will be placed within your infrastructure.
  • Detection techniques: opt for an IDS with diverse detection methods, combining signature-based, anomaly-based, and behavior-based techniques.
  • Customization: ensure the IDS allows customization of detection rules to fit your unique network environment.
  • Scalability: verify that the IDS can handle your network’s traffic volume without compromising performance.
  • Integration: check compatibility with other security tools for a comprehensive defense strategy.
  • Reporting and alerts: look for clear, actionable alerts and reporting capabilities compatible with your incident response processes.
  • Vendor support: evaluate the vendor’s update frequency and technical support availability.
  • Ease of use: consider user-friendly interfaces for effortless management.
  • Cost and budget: weigh the IDS’s cost against its value and effectiveness in meeting your security needs.
  • Reputation: research vendor reputation and reviews in the cybersecurity community for insights into system performance and reliability. 

IDS implementation best practices

Implementing an Intrusion Detection System (IDS) requires careful planning and consideration. Here are some best practices to follow when implementing IDS:

  1. Define clear objectives: set clear goals for IDS implementation based on risks and compliance needs to help guide your strategy accordingly. 
  2. Conduct security assessment: assess network vulnerabilities to strategically deploy IDS sensors in critical areas. 
  3. Develop deployment plan: create a detailed plan for IDS sensor placement, covering high-risk entry points and sensitive systems.
  4. Choose the right solution: select a suitable IDS solution considering scalability, compatibility, and integration capabilities.
  5. Optimize rules and signatures: customize IDS rules and signatures for your network, minimizing false positives and enhancing detection accuracy.
  6. Regularly update software: keep IDS software and signatures up to date with the latest patches and threat intelligence feeds.
  7. Monitor and analyze alerts: establish efficient workflows for handling IDS alerts and train your team to respond promptly.
  8. Integration: enhance security by integrating IDS with firewalls, SIEM, endpoint security, and threat intelligence.
  9. Regular testing: verify IDS capabilities through simulated attacks or vulnerability assessments.
  10. Staff training: invest in security team training for effective IDS management and threat response.
  11. Document and review processes: maintain updated documentation of IDS configuration, incident response, and customizations.


What is the difference between an IDS and an IPS?

An IDS passively monitors network traffic and generates alerts when it detects suspicious or potentially malicious activities. In contrast, an IPS actively monitors and can take immediate action to block or prevent detected threats, offering a more proactive approach to network security.

What is the difference between an IDS and a firewall?

An IDS monitors network traffic for suspicious or malicious activities and generates alerts when potential threats are detected. On the other hand, a firewall acts as a barrier between networks, controlling incoming and outgoing traffic based on predefined security rules, effectively blocking unauthorized access and malicious traffic.

Can IDSs be integrated with other cybersecurity technologies and tools?

Yes, Intrusion Detection Systems (IDS) can be integrated with other cybersecurity technologies and tools to enhance overall security capabilities and improve the effectiveness of threat detection and response.

How can IDSs facilitate incident response?

IDSs can facilitate incident response by continuously monitoring network traffic and endpoint activities for signs of suspicious or malicious behavior. When it detects a potential security incident, it alerts security personnel, enabling them to quickly identify and respond to threats, investigate the incident, and take appropriate actions. 

Final thoughts

Intrusion detection systems play a pivotal role in fortifying your organization’s cybersecurity defenses. They provide real-time threat detection, enable proactive defense, detect insider threats, facilitate compliance, aid in incident response, and enhance your security posture.

To harness the full potential of your IDS and protect yourself from the widest range of threats, you must consider your specific needs, such as your security goals and infrastructure.

If you seek expert advice on how to select, deploy, or optimize your intrusion detection system, CovertSwarm is here to assist. Simply contact us and a member of our team will find an empowering solution that keeps you one step ahead of potential intrusions.