What Is an Intrusion Detection System?

An intrusion detection system (IDS) is a vigilant application or device that proactively screens, monitors, and analyses a network against malicious threats. 

The cybersecurity landscape benefits from the distinct but interconnected safety features of intrusion detection and intrusion prevention systems (IPS). An IDS acts as the "watchful eye" that continuously monitors network activities and provides early warning of potential threats. Meanwhile, the IPS prevents and stops detected threats from causing harm to a network. 

Types of intrusion detection systems

IDS solutions come in different forms, each with its capabilities tailored to meet specific security requirements. Review two prevalent types of intrusion detection systems below:

• NIDS: Network intrusion detection systems are strategically placed within an organisation's internal network infrastructure to actively monitor and identify any malicious or suspicious traffic from devices connected to the network.

• HIDS: A host intrusion detection system (HIDS) safeguards all devices connecting to the internet and the organisation's internal network. It detects internal packets and additional malicious traffic missed by NIDS. HIDS also identifies host-based threats, like malware attempting to spread within an organisation's system.

How do intrusion detection systems work?

An IDS supports organisations in their cybersecurity strategies by offering assistance in one of three ways:

• Signature-based detection: The IDS examines all packets traversing an organisation's network and matches them against a database of known attack signatures through string comparison.

• Anomaly-based detection: The IDS compares definitions of what is normal with recorded events to spot deviations in network activity. Anomaly-based systems employ machine learning to establish a reference point for expected behaviour. This detection method can prove instrumental in combating novel threats. 

• Stateful protocol analysis: The IDS analyses observed events with predefined profiles of protocol activity that are safe or benign. The process repeats for every protocol state.

IDS vs. firewall: What’s the difference? 

An IDS passively observes network activity, alerting incident responders or security operations centre (SOC) analysts to potential threats. However, it does not offer protection for endpoints or networks beyond incident response.

In contrast, a firewall actively monitors and blocks threats to prevent incidents. It acts as a barrier, selectively allowing or blocking network traffic based on preconfigured rules.

Related terms

• CIA triad

• Computer forensic investigator

• Cybersecurity analyst

• Security engineer

• Information security analyst

• Cryptanalyst

Getting started with Coursera

Cybersecurity requires vigilance, precisely what intrusion detection systems (IDS) offer. The applications provide next-level security by screening, monitoring, and analysing networks to protect them from threats. 

Continue gaining knowledge and take the next step towards a career in cybersecurity by enrolling in the Google Cybersecurity Professional Certificate on Coursera. This certificate is your gateway to exploring job titles like security analyst SOC (security operations centre) analyst, and more. Upon completion, you’ll have exclusive access to a job platform with over 150 employees hiring for entry-level cybersecurity roles and other resources supporting your job search.