Understanding What Happens During a Third-Party Security Audit
Introduction & Purpose
Third-party audits are a core component of modern compliance programs. A successful audit confirms that your organization meets the requirements of security frameworks such as SOC 2, ISO 27001, NIST, and PCI DSS. Just as important, audits also strengthen internal governance and inspire confidence among customers, partners, and regulators.
This guide outlines the key phases of an external audit, explains what to expect during each phase, and offers best practices to ensure a smooth, effective audit experience. Understanding the audit lifecycle allows you to engage audit teams proactively, avoid surprises, and demonstrate readiness at every step.
Key Concept & Context
Audits typically follow a multi-phase process, regardless of framework. The process is designed to evaluate your compliance across three layers:
- Governance: Policies, procedures, risk management, and documentation.
- Operational: Actual control activities performed by teams.
- Technical: System-level evidence and security configurations.
Each phase of the audit builds on the previous one. Knowing what is expected and when enables better coordination and outcome management.
Practical Guidance: Key Phases of the Audit Process
A. Project Initiation & Planning
This foundational phase defines the scope and sets expectations:
- Schedule initial planning calls with the audit firm.
- Confirm the documented scope of the audit, including systems, teams, and timeframes.
- Establish communication channels and cadence.
- Clarify the “audit observation window” (when auditors will expect evidence to be from).
Note: Auditor styles and processes can vary. Aligning early on timelines, walkthrough preferences, and communication norms helps avoid delays later. These are also helpful criteria to evaluate when selecting an auditor.
B. Examination & Testing ("Audit Observation Window")
Auditors assess how well your controls are designed, implemented, and operating. This phase includes a structured evaluation across three layers:
- Governance Layer
Auditors review your risk register, policies, incident response plans, and other governance documents. They evaluate whether documentation accurately represents your compliance objectives and whether controls are mapped to framework requirements. - Operational Layer
Focuses on how controls are performed in practice. Auditors examine whether teams follow defined procedures and whether responsibilities are assigned and executed correctly. - Technical Layer
Technical testing includes system configurations, logs, access controls, vulnerability management, and encryption. Auditors will verify that your tools and platforms enforce security requirements as expected.
Trustero enables you to prepare for this stage by mapping policies to controls and generating evidence aligned with test procedures in advance.
C. Evidence Walkthroughs
During the observation window, auditors typically conduct one to three walkthrough sessions. These live, interactive reviews include:
- Real-time demonstration of how evidence aligns with controls.
- Clarification of control ownership, process steps, and system behavior.
- Opportunities to address misunderstandings or gaps on the spot.
Walkthroughs increase transparency and help resolve issues more efficiently than email exchanges alone.
D. Report & Certification Deliverables
The audit concludes with report preparation and final certification:
- A draft report is shared for review. This includes findings (if any), management responses, and auditor conclusions.
- Teams have an opportunity to review, clarify, or respond to findings.
- Once finalized, the report or certification (e.g., SOC 2 Type II Report, ISO 27001 Certificate) is issued.
Plan for a 4 to 8-week report timeline after audit fieldwork is complete. Align internal and external stakeholders on delivery expectations early in the process.
Conclusion
Security audits validate your organization's commitment to protecting systems and data. Understanding the phases of the audit process from planning through certification allows your team to prepare effectively, maintain confidence throughout the engagement, and avoid unnecessary delays.
By approaching the audit with transparency, coordination, and readiness, you increase the likelihood of a successful outcome and demonstrate that your compliance program is mature, repeatable, and audit-ready.