Security Due Diligence for M&A: What to Assess Before the Transaction Closes

Security due diligence is treated as a checkbox in most mergers and acquisitions. A questionnaire goes to the target, responses come back, someone in the deal team reviews them, and the deal proceeds. The problem is that a self-reported questionnaire tells you what a target believes about its own security posture, not what is actually there. By the time an acquirer discovers unpatched systems, unencrypted data stores, or a breach that occurred six months before close, the transaction has already settled.

We have seen this pattern repeatedly across different deal sizes and sectors. A mid-market business that looks clean on paper can carry years of accumulated technical debt, shadow IT systems that no one in security is aware of, and vendor relationships that expose customer data in ways that create regulatory liability the moment they become your liability too.

What a Security Review in M&A Should Actually Cover

Technical infrastructure is the starting point, but not the whole picture. At the infrastructure level you want to understand the patch posture of critical systems, the architecture of network segmentation (particularly whether operational and corporate environments are separated), and whether privileged access is managed or is the default state. These are quick indicators of hygiene. Poor hygiene in these areas reliably predicts problems in areas that are harder to assess.

Identity and access management deserves specific attention in any acquisition. Orphaned accounts, shared credentials, excessive privileged access, and the absence of multi-factor authentication on internet-facing systems are common findings that carry real risk. They are also findings that a target's security team may not be aware of, particularly in organisations that have grown by acquisition themselves and never normalised their directory environment.

Data, Compliance, and Regulatory Exposure

The most consequential security findings in M&A are often in the data and compliance layer, not the technical layer. An organisation that holds personal information under the Privacy Act and has not notified the Office of the Australian Information Commissioner of a past breach is carrying regulatory liability. An organisation that holds health information, financial data, or data from government clients may be subject to sector-specific requirements that the acquirer would inherit.

Data classification and data flows are frequently undocumented in mid-market businesses. Where data lives, who has access to it, what third parties process it, and whether those relationships are documented in compliant data processing agreements are all questions that need answers before close. If a target cannot answer these questions, that is itself a material finding, because it means you are acquiring not just the data but the uncertainty about what that data exposure is.

Vendor and Third-Party Risk

Third-party relationships multiply the exposure surface of any organisation. A target that uses a managed service provider with administrative access to its environment has effectively extended that environment to a third party. Whether that provider is subject to appropriate contractual controls, whether access is monitored, and whether the target has any visibility into the provider's own security posture are all questions that need to be on the table.

Software supply chain risk is an increasingly material consideration. Targets that have custom-developed software, particularly software with internet-facing components, should have that software reviewed for common vulnerability classes. Targets that rely heavily on third-party software-as-a-service platforms should have those vendor relationships evaluated for data residency, access controls, and business continuity provisions. These are not edge cases; they are normal features of most business IT environments.

How to Structure the Assessment

A security due diligence engagement in an M&A context is time-constrained by the deal timeline. It needs to be designed to produce the most material findings in the available window. We structure these engagements around a tiered approach: a rapid review of highest-risk indicators in the first phase, followed by deeper investigation of areas flagged in that review. The output is a risk-rated findings register that feeds into deal pricing, representations and warranties, and post-close remediation commitments.

The framing for the acquiring team matters. Security due diligence does not produce a pass or fail result. It produces a risk picture that informs negotiation. Known, quantifiable security debt is manageable. Unknown exposure is not, which is why the goal of the assessment is to reduce the unknown, not to produce a clean bill of health. Any firm that promises a clean bill of health from a time-boxed questionnaire review is not doing due diligence.

To discuss security due diligence for an upcoming transaction, contact Cyberlinx at info@cyberlinx.com.au.