How an IDS Works
An IDS can either be deployed as a:
- Network-based solution
- Host-based solution
In both deployment locations, it monitors network traffic and other malicious activity to identify potential intrusions and other threats to the monitored network or device. An IDS can use a couple of different means of identifying potential threats, including:
- Signature-Based: Signature-based detection mechanisms use unique identifiers to look for known threats. For example, an IDS may have a library of malware hashes that it uses to identify known malware attempting to infiltrate the protected system.
- Anomaly-Based: Anomaly-based detection depends on building a model of normal behavior within the network or protected device. It then looks for any deviations from this norm that could indicate a cyberattack or other incident.
Why use an Intrusion Detection System (IDS)?
Cyberattacks have reached record levels in recent years. Data from the Identity Theft Resource Center found that data breaches in 2024 were the second highest on record, behind only 2023. But, while the number of data breaches remained roughly the same in 2024 as in 2023, the number of victims increased significantly, with attacks affecting many more people.
Data breaches and unauthorized access to your corporate network can have significant consequences, with:
- Financial costs
- Reputational damage
- Loss of customers
Organizations must develop robust security strategies to protect their corporate data. There are many methods attackers use to target corporate networks.
With attack vectors such as phishing and other social engineering attacks, unsecured endpoints, software application vulnerabilities, SQL injection, cross-site scripting, insider threats, and more continuously targeting enterprise IT, security teams need tools to monitor network traffic and automate intrusion detection.
An IDS monitors networks for suspicious behavior that needs to be escalated through further investigation or immediate preventative measures (blocking traffic, quarantining files, etc.). IDSs also support compliance by protecting your data and providing reporting.
While generally seen as an incident response trigger, IDSs also provide valuable data about your networks to help identify vulnerabilities and prevent attacks.
The 8 Types of Intrusion Detection Systems
There are many types of intrusion detection systems. From simple antivirus software applications to comprehensive monitoring systems that cover your entire organization: From cloud-based intrusion detection and local on-premises systems, to software applications installed on endpoints and physical hardware placed throughout the network.
The most common ways of distinguishing between the different types of intrusion detection systems are where they are located in the network, and the method by which they identify potential threats.
Network Location
The two most common types of intrusion detection systems based on network location are Network Intrusion Detection Systems (NIDS) and Host-based Intrusion Detection Systems (HIDSs).
Network Intrusion Detection Systems
NIDSs are most commonly positioned at the network perimeter behind firewalls to flag inbound and outbound traffic. However, they can also be used more centrally to target insider threats or compromised accounts. NIDSs are often “out of band” to monitor traffic without impacting network performance.
This means they copy data packets for inspection rather than analyze the original.
Host-Based Intrusion Detection Systems
HIDSs are positioned at specific endpoints (e.g., router, server, etc.) and only monitor traffic passing through the device. HIDSs are often used to periodically monitor vital operating systems, looking for suspicious activities such as edited log files or configuration changes.
It is not uncommon for security teams to rely on NIDSs and HIDSs. Utilizing NIDSs for big-picture information on the entire network and HIDSs for detailed data related to the most important systems.
Other types of IDS include:
- Protocol-based Intrusion Detection System (PIDS): Tracks connection protocols such as HTTP or HTTPS.
- Application Protocol-based Intrusion Detection System (APIDS): Monitors application-specific protocols, for example, protecting against SQL injections.
Detection Method
The two main types of intrusion detection systems based on detection methods are signature and anomaly approaches.
Signature-Based IDS
As attack vectors are identified and studied, we are able to identify the specific patterns they follow.
These are known as signatures, and signature-based IDSs inspect network traffic to identify the patterns associated with potential threats.
To implement signature-based detection, the IDS requires an up-to-date threat database containing the latest known attack signatures. This approach is inherently more reactive. It requires that threats be observed and their signatures be identified and input into security tool databases.
You are susceptible to new attacks and must regularly update your IDS to ensure the best protection.
Anomaly-Based IDS
In contrast, anomaly-based methods take a more proactive approach to IDS, identifying any suspicious activity regardless of whether it follows a previously seen threat.
Anomaly-based IDS uses machine learning behavioral analysis to monitor your network and develop a model for normal network activity. By learning what safe network traffic looks like, the technology can identify instances that deviate from the model, potentially signaling an attack.
As it is based purely on identifying real-time anomalous behavior, not known signatures, this approach can catch new threats like zero-day exploits.
But, the quality of anomaly-based IDS depends on how it is implemented. The method can be prone to sending false positives that incorrectly class behavior as suspicious and waste the time and resources of security teams. Taking into account contextual information can improve performance, providing a better understanding of normal activities and reducing the rate of false positives.
Other Detection Methods
Other types of intrusion detection systems incorporate lesser-used detection methods, such as:
- Reputation-based detection: Blacklists specific IP addresses and domains known for malicious activities and blocks all traffic from them.
- Stateful protocol analysis: Blocks traffic depending on protocol behavior. For example, blocking an IP address that makes a large number of requests in a short period to prevent denial-of-service attacks.
7 Most Common Challenges of IDS
An IDS can be a valuable component of a corporate security architecture. But, organizations commonly face challenges when using an IDS, including the following:
- Incorrect Detections: IDS can use a combination of signature and anomaly detection mechanisms, and both can make mistakes if the firewall design isn’t hardened. Signature detection is more prone to false negatives when a new malware variant doesn’t have a signature in its database. Anomaly detection can have false positives if a benign anomaly is mistakenly classified as a potential threat.
- Alert Volumes: An inferior IDS design often generates large volumes of alerts that security personnel need to search through and triage. Security teams can easily become overwhelmed, and, if many alerts are false positives, they may start ignoring them, resulting in missed intrusions.
- Alert Investigation: IDS alerts often provide basic information about a security incident but may lack important context. As a result, security personnel may invest significant time and effort investigating and understanding an alert before triggering incident response or dismissing it as a false positive.
- No Threat Prevention: An IDS is designed to identify a potential threat and alert security teams about it. It does nothing to actually prevent threats, leaving a window to attack the organization before manual response operations are triggered. If the alert is missed or ignored, the security team may not even respond to the incident.
- Alert Fatigue: IDS is only designed to alert organizations. By lacking the automated response of an integrated IDS+IPS (Intrusion Prevention Service), security teams are burdened with higher workloads. And in many cases, these teams will invariably ignore or mute alerts based on being overloaded with too much ‘data’ to investigate.
- Configuration and Maintenance: To properly identify potential security risks, an IDS must be properly deployed, configured, and maintained. This requires specialized expertise and resources that might otherwise be used elsewhere.
- Resource Requirements: An IDS may consume significant resources to identify threats, especially if it has a large signature dictionary or advanced anomaly detection algorithms. These could degrade system performance or result in poor performance if an IDS is deployed in-line. Additionally, signature libraries must be frequently updated to identify the latest threats.
Intrusion Detection System (IDS) vs. Intrusion Prevention System (IPS)
As noted, an IDS only generates alerts. It does not intercept or block threats.
A similar security tool that provides additional capabilities is an Intrusion Prevention System (IPS), which identifies potential threats and automatically intercepts them. This could be directly responding via blocking traffic or indirectly responding by activating other tools.
These systems accelerate threat response even more than an IDS, preventing attacks before they have a chance to infiltrate your network. But, automated responses mean that false positives will block legitimate traffic, impacting operations. IDS vs. IPS creates a trade-off between the speed of protection and blocking legitimate traffic, between security and usability.
Challenges and Limitations of IDS
While IDSs offer a range of threat protection benefits, implementation challenges and performance limitations exist. These include:
- Slowing down network performance by inspecting traffic.
- Complex installation and determining the optimal implementation in terms of IDS solution types.
- Regular updates and maintenance to ensure your IDS has the latest signatures and provides comprehensive coverage.
- Implementation requires a lot of work for a detection system that doesn’t prevent attacks by itself.
- False positives waste IT resources that could be spent investigating genuine threats and potentially lead to alert fatigue and underestimating real attacks.
There are also specific evasion tactics attackers can utilize to bypass IDSs. Methods include:
- A Distributed Denial-of-Service (DDoS) attack is used as a decoy to take IDSs offline, followed by a genuine attack once defenses are down.
- Obscuring malware signatures through fragmentation and finding inventive ways to split the payload across different packets.
- Bypassing IDSs by using encrypted protocols.
- Address spoofing or proxy servers are used to hide the source of traffic.
Selecting an IDS/IPS Solution with Check Point
Check Point’s next-generation firewall, Quantum, incorporates intrusion prevention systems to detect and prevent attempts to gain unauthorized access. Quantum simplifies IPS management with automatic updates to maintain comprehensive threat databases and protect your systems.
However, if you want to go further and integrate all the security functionality you need into a single platform while maintaining network performance consider Harmony SASE – the future of cybersecurity.
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