What Is Incident Response?

Incident response is the structured process an organization uses to detect, contain, and recover from a security incident. Incident response applies a defined set of phases, a trained team, and a written plan to limit the damage of a breach and restore normal operations. The National Institute of Standards and Technology (NIST) defines this process in Special Publication 800-61, and the SANS Institute describes a parallel six-step model.

This article defines incident response, explains why it matters, sets out the NIST and SANS phases, describes the incident response team or Computer Security Incident Response Team (CSIRT), explains the incident response plan, and covers playbooks. A required table summarizes the phases.

Each section states one part of the topic and connects it to the goal of limiting damage and recovering from an incident. The result is a complete account of what incident response is, the phases it follows, and the people and documents that carry it out.

What Is Incident Response?

Incident response is the structured process an organization uses to detect, contain, eradicate, and recover from a security incident while limiting damage and restoring operations. Incident response follows defined phases, executed by a trained team using a written plan. The defining traits of incident response are listed below:

• A structured process follows defined phases rather than an improvised reaction to each incident.
• Detection and containment identify an incident and stop it from spreading further into systems.
• Eradication and recovery remove the threat and restore affected systems to normal operation.
• A trained team and plan carry out the process using documented roles and procedures.

Incident response handles the security incidents that other controls fail to prevent, building on the broader principles in the fundamentals of computer security. A common trigger for incident response is a data breach, in which attackers access protected information.

Why Does Incident Response Matter?

Incident response matters because it limits the damage of a security incident, shortens recovery time, and reduces the financial and reputational cost of a breach. A planned response contains a threat before it spreads, whereas an unplanned reaction lets damage grow. The reasons incident response matters are listed below:

• Limited damage results when containment stops an incident before it reaches more systems and data.
• Faster recovery follows from defined procedures that restore operations without delay or guesswork.
• Reduced cost comes from shorter breach duration, since a contained incident affects fewer records.
• Evidence preservation supports investigation, legal action, and reporting after the incident closes.

Incident response reduces the time an attacker remains in a network, which directly lowers the scope of a data breach. A faster response depends on early detection, the role of a security information and event management system that aggregates and alerts on suspicious activity.

What Are the NIST Incident Response Phases?

The NIST incident response process defines four phases: preparation, detection and analysis, containment, eradication, and recovery, and post-incident activity. NIST Special Publication 800-61 sets these phases as a continuous cycle rather than a single pass. The NIST phases are listed below:

• Preparation builds the team, plan, tools, and training before any incident occurs.
• Detection and analysis identifies an incident, determines its scope, and confirms it is genuine.
• Containment, eradication, and recovery stops the spread, removes the threat, and restores systems.
• Post-incident activity reviews the response to capture lessons and improve future readiness.

The NIST phases form a loop, since post-incident activity feeds back into preparation for the next event, according to NIST Special Publication 800-61. Detection in this model often begins with alerts from an intrusion detection and prevention system that flags suspicious traffic.

What Are the SANS Incident Response Phases?

The SANS Institute defines six incident response phases: preparation, identification, containment, eradication, recovery, and lessons learned, summarized by the acronym PICERL. The SANS model expands the NIST process into six discrete steps. The SANS phases are listed below:

• Preparation establishes the policies, team, and tools needed before an incident occurs.
• Identification detects and confirms that a security incident has taken place.
• Containment isolates affected systems to stop the incident from spreading.
• Eradication removes the cause, such as malware or a compromised account, from the environment.
• Recovery restores systems to normal operation and confirms they are clean.
• Lessons learned reviews the incident to improve the plan and prevent recurrence.

The SANS PICERL model and the NIST process describe the same lifecycle, differing only in how they group the steps, according to the SANS Institute. Both place preparation first and a review last, treating incident response as a repeatable cycle.

Incident Response Phases Comparison Table

What Is an Incident Response Team or CSIRT?

An incident response team, also called a Computer Security Incident Response Team (CSIRT), is the group of people responsible for detecting, managing, and resolving security incidents. A CSIRT combines technical, managerial, and communication roles to execute the response plan. The roles within an incident response team are listed below:

• An incident response manager leads the team, coordinates the response, and makes containment decisions.
• Security analysts investigate the incident, analyze evidence, and identify the scope of compromise.
• Forensic specialists preserve and examine evidence to determine how the incident occurred.
• Communication and legal roles handle notifications, regulatory reporting, and stakeholder updates.

A CSIRT carries out every phase of the response, drawing on the detection data that a SIEM platform centralizes. The team’s findings often feed a security audit that evaluates how controls performed during the incident.

What Is an Incident Response Plan?

An incident response plan is the written document that defines how an organization detects, responds to, and recovers from security incidents, including roles, procedures, and communication. An incident response plan turns the response process into documented, repeatable steps. The components of an incident response plan are listed below:

• Roles and responsibilities assign each team member specific duties during an incident.
• Detection and reporting procedures define how incidents are identified and escalated.
• Containment and recovery steps set out the actions to stop and reverse an incident.
• Communication protocols specify who is notified, including management, regulators, and affected parties.

An incident response plan documents the procedures the CSIRT follows, a requirement of frameworks such as ISO 27001 and NIST. Testing the plan through exercises is one objective evaluated during a security audit, which measures readiness against a standard.

What Are Incident Response Playbooks?

An incident response playbook is a detailed, step-by-step procedure for handling a specific type of incident, such as ransomware, phishing, or a denial-of-service attack. A playbook translates the general plan into precise actions for one incident category. The traits of a playbook are listed below:

• Incident-specific steps define exact actions for one threat type, removing guesswork during a response.
• Defined triggers state the conditions under which the playbook is activated.
• Assigned actions map each step to a responsible role on the incident response team.
• Containment and recovery guidance tailors the response to the behavior of the specific threat.

A playbook for a malware incident specifies isolation and cleanup steps similar to the process to remove malware from a PC, scaled to an organization. Playbooks reduce response time because the team follows a prepared procedure rather than deciding actions during the incident.

How Does Incident Response Fit Into a Security Program?

Incident response is the reactive layer of a security program that operates after preventive and detective controls, completing the cycle of protect, detect, and respond. Incident response depends on the detection capabilities and policies that surround it. The connections to a security program are listed below:

• Preventive controls such as firewalls and access control reduce the number of incidents that reach the team.
• Detective controls such as monitoring and logging supply the alerts that trigger a response.
• The incident response process reacts once an incident is confirmed, containing and resolving it.
• Post-incident review feeds findings back into preventive and detective controls.

Incident response works alongside the detection provided by an IDS and IPS and the correlation of a SIEM, which together surface the events a team investigates. The weaknesses that lead to incidents are catalogued through security vulnerability management and tested with penetration testing.

What Are Common Types of Security Incidents?

Common types of security incidents include malware infections, ransomware, phishing, data breaches, denial-of-service attacks, and unauthorized access. Each incident type calls for a tailored playbook within the response plan. The common incident types are listed below:

• Malware and ransomware infect systems to damage data or encrypt it for extortion, requiring isolation and recovery from backups.
• Phishing deceives users into revealing credentials, requiring credential resets and review of accessed accounts.
• Data breaches expose protected information, requiring scope analysis and regulatory notification.
• Denial-of-service attacks disrupt availability, requiring traffic filtering and upstream mitigation.
• Unauthorized access uses stolen credentials or unpatched flaws, requiring account lockout and access review.

Each incident type maps to a dedicated playbook, since the containment and recovery steps differ by threat. A ransomware incident, for example, follows isolation and restoration steps similar to the process to remove malware from a PC, scaled across an organization and informed by SIEM alerts.

What Tools Support Incident Response?

Incident response is supported by SIEM platforms, endpoint detection and response, intrusion detection systems, and security orchestration, automation, and response (SOAR) tools. These tools supply the detection data and automation a response team depends on. The supporting tools are listed below:

• SIEM platforms aggregate logs from across the environment and generate the alerts that trigger a response.
• Endpoint detection and response (EDR) provides device-level visibility to detect and contain threats on endpoints.
• Intrusion detection and prevention systems flag and block suspicious network traffic during an incident.
• SOAR platforms automate repetitive response actions and orchestrate steps across multiple tools.

A SIEM centralizes the detection data, while endpoint security tools and an IDS and IPS supply device and network visibility. Together these tools shorten the time from detection to containment, which directly limits incident damage.

Key Takeaways

• Incident response is the structured process to detect, contain, and recover from a security incident.
• It matters because it limits damage, shortens recovery, and reduces breach cost.
• NIST defines four phases: preparation, detection and analysis, containment through recovery, and post-incident activity.
• SANS defines six phases under the acronym PICERL.
• A CSIRT is the team that carries out the response using a written plan.
• Playbooks give step-by-step procedures for specific incident types.

Last Thoughts on Incident Response

Incident response is the structured process an organization uses to detect, contain, and recover from a security incident while limiting damage and restoring operations. NIST Special Publication 800-61 defines four phases and the SANS PICERL model defines six, both treating the response as a repeatable cycle that ends with a review.

A Computer Security Incident Response Team executes the process using a written plan and incident-specific playbooks. Readers can continue with the guide to a SIEM, the explanation of a data breach, the overview of a security audit, or the guide to cybersecurity.