How to Build an Incident Response Plan: A Step-by-Step Guide

When a security incident occurs, the quality of your response determines whether it becomes a minor disruption or a business-threatening event. Organizations with a documented and practiced incident response plan recover faster and suffer less damage.

This guide walks you through building an incident response plan based on the NIST Computer Security Incident Handling Guide (SP 800-61).

Why You Need an Incident Response Plan

Without a plan, incident response becomes reactive and chaotic. Teams waste time figuring out who to contact, what actions to take, and how to communicate — all while the incident escalates.

A documented plan provides:

• Clear roles and responsibilities — Everyone knows their job during an incident
• Faster containment — Predefined procedures reduce decision-making time
• Consistent communication — Stakeholders receive timely, accurate updates
• Legal protection — Documented response shows due diligence
• Continuous improvement — Post-incident reviews prevent repeat occurrences

The Six Phases of Incident Response

Phase 1: Preparation

Preparation happens before any incident occurs. This is where you build the foundation.

Build your incident response team (IRT):

• Incident Commander — Leads the response and makes decisions
• Security Analyst — Investigates the technical details
• Communications Lead — Manages internal and external messaging
• Legal Counsel — Advises on regulatory obligations
• IT Operations — Handles system changes and restores
• Executive Sponsor — Authorizes resources and major decisions

Prepare your tools and resources:

• Secure communication channel (do not rely on potentially compromised systems)
• Forensic imaging tools
• Network and endpoint monitoring dashboards
• Contact list for all team members, vendors, and authorities
• Pre-drafted communication templates

Phase 2: Detection and Analysis

The faster you detect an incident, the less damage it causes. This phase focuses on identifying that an incident has occurred and understanding its scope.

Common detection sources:

• Security Information and Event Management (SIEM) alerts
• Endpoint detection and response (EDR) notifications
• User reports of suspicious activity
• External notifications from partners, customers, or law enforcement
• Automated threat intelligence feeds

When an alert fires, determine:

1. Is this a true positive or a false alarm?
2. What systems are affected?
3. What data may be at risk?
4. When did the incident begin?
5. Is it still active?

Classify the severity:

• Critical — Active data breach, ransomware spreading, production systems down
• High — Confirmed compromise of a single system, no lateral movement detected
• Medium — Suspicious activity that may indicate compromise, investigation needed
• Low — Policy violation or minor anomaly with no evidence of compromise

Phase 3: Containment

Containment limits the damage and prevents the incident from spreading. You need both short-term and long-term containment strategies.

Short-term containment (immediate):

• Isolate affected systems from the network
• Block malicious IP addresses and domains
• Disable compromised user accounts
• Redirect traffic away from compromised servers

Long-term containment:

• Apply temporary patches
• Rebuild compromised systems from clean images
• Implement additional monitoring on affected segments
• Rotate all credentials that may have been exposed

Important: Do not wipe systems before collecting forensic evidence. Image drives before rebuilding.

Phase 4: Eradication

After containing the incident, remove the threat completely.

• Identify the root cause of the compromise
• Remove malware, backdoors, and unauthorized accounts
• Patch the vulnerabilities that were exploited
• Verify that all attacker footholds have been eliminated
• Scan the entire environment for indicators of compromise (IOCs)

Phase 5: Recovery

Restore systems to normal operation with confidence that the threat has been eliminated.

• Restore systems from clean backups
• Bring systems back online in order of business priority
• Monitor restored systems closely for signs of reinfection
• Verify data integrity after restoration
• Gradually reduce enhanced monitoring as confidence grows

Phase 6: Lessons Learned

This phase is frequently skipped but is the most valuable for long-term improvement.

Conduct a post-incident review within one week:

• What happened? (Timeline of events)
• What went well in the response?
• What could be improved?
• Were there detection gaps?
• Did the plan work as expected?
• What changes are needed to prevent recurrence?

Document everything and update your incident response plan based on findings.

Incident Response Plan Template

Your written plan should include these sections:

1. Purpose and scope — What the plan covers and who it applies to
2. Incident classifications — Severity levels and criteria
3. Roles and responsibilities — The IRT roster with contact information
4. Detection procedures — How incidents are identified and reported
5. Containment procedures — Step-by-step containment actions by incident type
6. Communication plan — Who to notify, when, and how
7. Escalation paths — When to involve leadership, legal, or law enforcement
8. Recovery procedures — Steps to restore normal operations
9. Evidence handling — Chain of custody and forensic procedures
10. Review schedule — When the plan will be tested and updated

Testing Your Plan

A plan that has never been tested will fail when you need it most.

Testing methods:

• Tabletop exercises — Walk through scenarios verbally with your IRT (do quarterly)
• Simulation drills — Test procedures in a controlled environment (do biannually)
• Red team exercises — Simulate real attacks to test detection and response (do annually)

Frequently Asked Questions

How often should I update my incident response plan?

Review and update at least annually, and after every significant incident or organizational change.

Do small businesses need an incident response plan?

Absolutely. Small businesses are frequent targets precisely because attackers assume they lack formal response procedures.

Should I involve law enforcement after a breach?

In many jurisdictions, breaches involving personal data require notification to authorities. Even when not required, law enforcement can provide intelligence that helps your investigation.

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