Incident Response: A Step-by-Step Guide for Security Teams

Classification: PUBLIC
Category: Security Operations
Reading Time: 4 min

What Is Incident Response?

Incident Response (IR) is the organized approach to detecting, containing, and recovering from cybersecurity incidents. A well-prepared incident response plan can mean the difference between a minor security event and a catastrophic data breach. The NIST (National Institute of Standards and Technology) framework defines four phases of incident response.

Phase 1: Preparation

Preparation is the most critical phase, yet often the most neglected. Before any incident occurs, organizations should:

Establish an IR team with clearly defined roles and responsibilities
Create and maintain an IR plan that documents procedures for different incident types
Deploy monitoring tools such as SIEM (Security Information and Event Management) systems, EDR solutions, and network monitoring
Conduct tabletop exercises — simulate incidents to test the team's readiness and identify gaps
Maintain an asset inventory — you cannot protect what you don't know exists

Phase 2: Detection and Analysis

This phase involves identifying potential security incidents and determining their scope and severity:

Monitor alerts from security tools (IDS/IPS, firewalls, EDR)
Correlate events across multiple data sources to distinguish real incidents from false positives
Classify the incident based on severity (Critical, High, Medium, Low)
Document everything — maintain a detailed timeline of events and actions taken

Common indicators of compromise (IoCs) include unusual outbound network traffic, unexpected system file changes, anomalous login patterns, and unexplained privilege escalations.

Phase 3: Containment, Eradication, and Recovery

Short-Term Containment

Immediately isolate affected systems to prevent the incident from spreading. This may include disconnecting compromised machines from the network, blocking malicious IP addresses, or disabling compromised accounts.

Eradication

Remove the threat from all affected systems. This includes deleting malware, closing backdoors, patching exploited vulnerabilities, and resetting compromised credentials.

Recovery

Restore affected systems to normal operation. Rebuild compromised systems from clean backups, implement additional monitoring on recovered systems, and gradually restore network connectivity while watching for signs of reinfection.

Phase 4: Post-Incident Activity

The lessons learned phase is where organizations improve their defenses:

Conduct a post-mortem within 48 hours of incident resolution
Document the full timeline, root cause, and remediation steps
Update the IR plan based on lessons learned
Share intelligence with relevant communities (ISACs, CERTs) to help others defend against similar threats

Key Metrics to Track

Mean Time to Detect (MTTD) — How quickly you identify incidents
Mean Time to Respond (MTTR) — How quickly you contain and remediate
False Positive Rate — Percentage of alerts that aren't real incidents

Aegis Core provides tools to help with incident investigation. Use IP Intelligence to trace suspicious IPs and Domain Analyzer to investigate potentially malicious domains.