For CISOs, mergers and acquisitions (M&A) bring both potential and risk. These deals can drive growth, but they also open the door to serious cybersecurity threats that may derail the transaction. Strong due diligence, smart risk planning, and a shared security mindset can help keep deals on track and protect the business.

Key cybersecurity risks in M&A

1. Inherited vulnerabilities: Acquiring a company means inheriting its existing cybersecurity weaknesses. If the target company has unresolved security issues, these become the acquirer’s responsibility. For instance, undisclosed data breaches or outdated systems can pose immediate threats post-acquisition.

2. Data integration challenges: Merging IT systems can lead to data silos and integration difficulties. Inconsistent data protection measures between the two entities can expose sensitive information during and after the integration process.  

3. Regulatory compliance issues: Different jurisdictions have varying data protection regulations. An acquisition can inadvertently lead to non-compliance if the target company operates under different regulatory standards. This is particularly relevant in cross-border M&A activities. 

4. Cultural misalignment: Divergent organizational cultures, especially regarding cybersecurity priorities, can hinder the implementation of unified security policies and procedures. This misalignment can create gaps that adversaries might exploit.

Small businesses are often operating on thin cybersecurity margins, if any at all. “In more than 150 cyber assessments for small businesses (typically revenue in the $10–150 million range), we’ve found only a handful that operate above the cyber poverty line,” said Brad Strahorn, Managing Partner, Black Creek Cyber Security. While that doesn’t necessarily spell disaster since basic improvements like MFA are often within reach, Strahorn warns that cultural signals can be more troubling. “What does raise concern is when the culture signals risk: vague answers, low awareness, or leadership that doesn’t prioritize security.” Technically, he adds, the most common red flags include poor asset inventory management, the absence of an incident response plan, and under-managed endpoints.

Merging security cultures

Merging two companies means merging two security cultures. That is often harder than unifying tools or policies. While the technical side of post-M&A integration is important, it’s the human and procedural elements that often introduce the biggest risks.

“When CloudSploit was acquired, one of the most underestimated challenges wasn’t technical, it was cultural,” said Josh Rosenthal, Holistic Customer Success Executive at REPlexus.com. “Connecting two companies securely is incredibly complex, even when the acquired company is much smaller.”

Too often, the focus in M&A deals lands on surface-level assurances like SOC 2 certifications or recent penetration tests. While important, those are “table stakes,” Rosenthal noted. “They help, but they don’t address the real friction: mismatched security practices, vendor policies, and team behaviors. That’s where M&A cybersecurity risk really lives.”

As AI accelerates the speed and scale of attacks, CISOs are under increasing pressure to ensure seamless integration. “Even a phishing attack targeting a vendor onboarding platform can introduce major vulnerabilities during the M&A process,” Rosenthal warned.

To stay ahead of these risks, he said, smart security leaders need to dig deeper than documentation. “CISOs should proactively evaluate how security is actually operationalized, not just documented. That includes looking at day-to-day SOPs and incident response habits, vendor access management practices, and cultural alignment around risk tolerance.”

Because in a merger, Rosenthal concluded, “your weakest link is rarely the code, it’s usually people and process.”

Security integration as partnership, not imposition

When integrating an acquired company, ensuring a cohesive security posture is both a technical and cultural exercise, says Michael Miora, CEO at InfoSec Labs. “We learned about the acquired company’s security posture during the due diligence and deep dive phase,” he explains. This involved a thorough analysis of the target’s architecture, controls, third-party dependencies, and policies.

Rather than treating the process as a one-way imposition, Miora emphasizes that it was approached as a partnership. “We didn’t approach this as a top-down imposition. Instead, we treated it as a partnership, respecting cultural and operational differences while steering toward a common security standard,” he says.

The team began by comparing the acquired company’s practices against their own internal baseline standards. “Where gaps existed, we collaborated to build a phased integration plan focusing on key controls,” Miora notes. This plan wasn’t static. Joint tabletop exercises were conducted to identify remaining blind spots and refine incident management protocols and processes.

Ultimately, Miora says, success hinged on prioritizing issues thoughtfully and aligning the two organizations around shared security goals, while acknowledging the realities of different starting points.

Building a unified GRC strategy

In mergers and acquisitions, aligning governance, risk, and compliance (GRC) frameworks is not just a task to check off. It takes careful balance and planning.

“Each company has its own way of doing things,” said Biljana Cerin, CEO at Ostendo Consulting. “I usually knew the acquiring company well. But I had to look more closely at how the acquired company handled its controls, policies, risk processes, and reporting.”

That close scrutiny is essential because the two sides often operate at different speeds. According to Cerin, “The acquiring company often had more complex GRC needs. The acquired company was usually leaner and more flexible.” The real challenge, they explained, lies in merging these systems in a way that upholds the acquiring company’s standards without stifling the agility or culture of the newly acquired business.

Conflicts were common, especially around compliance areas like data governance, privacy regulations, and security frameworks. “To handle this, we needed a balanced approach,” Cerin said. “We respected the acquired company’s way of working but made sure they aligned with the stricter rules of the acquiring company.”

At the heart of that balancing act was the CISO. “The CISO played a key role,” Cerin emphasized. “They had to explain the goals of integration while also understanding the acquired company’s culture and needs.” This wasn’t just about communication, it required a fact-based understanding drawn from objective, evidence-based reviews.

Once the deal closed, the work of integration truly began. Cerin described the post-acquisition process as one focused on unification: “We worked to bring together risk registers, audit trails, and reporting structures. The goal was a single, unified system. We aligned risk items, made audit records consistent, and changed reporting lines to give better oversight of risk and compliance across both companies.”

Again, the CISO’s leadership was vital, not just in technical terms, but in fostering trust and cooperation. “They helped both sides understand each other and work together,” Cerin said. “This helped meet business needs while making the transition smoother.”

Still, some challenges persisted. “At times, parts of the acquired company remained siloed,” Cerin admitted. “But once the teams understood the reasons for integration, things got better. Still, in many cases, silos remain even years later.” Addressing those long-term gaps, they added, requires “ongoing control testing, targeted risk reviews, and open conversations about problems.”

In other words, successful GRC integration isn’t just a one-time effort, it’s a sustained commitment to both structure and empathy.

What happens after the deal?

After a merger or acquisition, the work of unifying security teams, tools, and policies begins, and it’s rarely simple. Sean R Turner, CISO at Twinstake, who navigated this process firsthand, said the complexity often depends on what kind of pressure the organization is under.

“Teams can be quite easy if there isn’t an immediate requirement to slash costs nor revoke autonomy,” Turner said. “People can carry on doing what they do as a vocation, and it’s just the leadership that reshuffles in the short term.”

But while people might stay in place, the technology stack almost never does.

“Tools require a review of value, contractual obligations, sometimes licensing terms, and identity management processes,” he said. The goal is to identify redundancies, resolve conflicts, and ultimately rationalize the combined environment. That can become especially tricky when identity and access management (IAM) systems aren’t aligned, or worse, incompatible.

Policy alignment, meanwhile, is often more political than technical. “Policies will require a collaborative review and some decision-making ability that may spill well outside security,” Turner said.

He pointed to several key systems as early touchpoints for untangling the technical sprawl that comes with M&A: “HRIS, business information systems, IAM and end user computing are good places to start attacking the technology problems associated with crashing systems and teams together.”

However, these systems often fall under the CIO’s domain, depending on how the organizations are structured. That can leave the CISO or head of security in the smaller company navigating a power dynamic.

“You may well end up with a smaller business CISO or head of security having to work with peers in multiple C-suite roles in the acquiring business to affect change,” Turner said.

The lesson? The post-M&A integration phase isn’t just a technical exercise. It requires soft skills, diplomacy, and a clear-eyed understanding of organizational politics.

Listen to customers

After an acquisition, one of the first and most important steps is to listen, especially to customers. “I would make sure to talk to the top 10 customers and understand their wants and desires around your solutions,” said Michael Malone, CEO of Lumifi Cyber. “It gives guidance to your team.” But those conversations aren’t just about roadmap alignment, they’re also an opportunity to assess risk. “Make sure you look at their cyber posture to see if prior activity or problems occurred, sometimes that gets omitted in due diligence,” Malone added.

Surprises, Malone noted, are inevitable. “Expect to learn things you didn’t know before, and accept these discoveries as part of the post-acquisition process,” he said. Rather than seeing unexpected issues as setbacks, Malone stressed the importance of building a resilient team. “The best way to navigate surprises or little bumps in the road is to build an excellent team at every level, especially by elevating and empowering team members from the acquired entity so they have the confidence to help fix issues as they arise.”

Throughout that process, customer relationships must remain front and center.

“The most important lesson we’ve learned from the post-acquisition period is that face-to-face relationships with customers pay huge dividends,” Malone said. “There’s no substitute for sitting down with a newly acquired customer and simply listening and learning.” That means investing heavily in outreach, whether it’s in-person visits, webinars, or on-site events. “Communication strategy has to include immense outreach, they all matter and make a tremendous difference,” Malone said. “It’s important to recognize that change is difficult, and it’s incumbent on the acquiring party to hear concerns, be transparent, and educate on changes, benefits, and future direction.”

Strategies for mitigating cybersecurity risks

CISOs should consider the following strategies:

1. Early involvement in due diligence: Engage the cybersecurity team at the outset of M&A discussions. Conduct assessments of the target company’s security posture, including policies, incident history, and compliance status. This proactive approach helps identify potential deal-breakers early. 

2. Comprehensive risk assessments: Beyond technical evaluations, assess the target company’s risk management frameworks, third-party relationships, and data governance practices. Understanding these aspects provides a holistic view of potential vulnerabilities. 

3. Develop integration plans with security in mind: Prioritize the creation of detailed integration plans that address cybersecurity concerns. This includes aligning security policies, standardizing protocols, and ensuring consistent compliance measures across both organizations.

4. Implement Identity and Access Management (IAM): Control and monitor access to critical systems during the integration phase. IAM practices prevent unauthorized access and reduce the risk of insider threats.

5. Secure legal protections: Incorporate specific cybersecurity representations, warranties, and indemnities in the M&A agreement. These legal provisions offer recourse if undisclosed security issues surface post-acquisition. 

6. Continuous monitoring and post-acquisition audits: Establish ongoing monitoring mechanisms to detect and respond to threats promptly. Conduct post-acquisition security audits to ensure that integration has not introduced new vulnerabilities.

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