The Hidden Risk of Legacy Networks Following Mergers and Acquisitions

Mergers and acquisitions are a frequent growth strategy in healthcare, particularly as hospitals and health systems continue to acquire independent physician practices. While these transactions promise operational efficiencies and expanded care delivery, they often introduce an underestimated risk: the legacy network environment inherited from the acquired practice.

These legacy networks – especially those managed by a third‑party IT vendor – linger in the now control of the acquiring entity longer than necessary after closing. When those networks are not tightly governed, clearly scoped from a security‑responsibility perspective and quickly migrated, they can become a significant cyber and compliance exposure for the acquiring health system.

The Risk: Lingering Networks

In today’s threat landscape, the most dangerous network may be not the one you built but the one you inherited.

Small physician practices typically operate with lean IT resources. Their networks may rely on aging hardware, minimal segmentation, shared credentials or security tools that differ dramatically from the acquiring enterprise’s standards. Once acquired, these environments may remain operational to support continuity of care, billing workflows or legacy electronic health record (EHR) access – sometimes for months or even years.

During this transition period, the legacy network may:

• Remain connected (directly or indirectly) to the acquiring enterprise network
• Continue handling electronic protected health information
• Be administered by a third‑party IT vendor with limited oversight
• Lack uniform monitoring, logging or incident response integration

Attackers increasingly target these environments either as a crime of opportunity or because they offer a path of least resistance into larger, better‑defended health systems with deeper pockets to extort.

Third‑Party IT Vendors: Responsibility Gaps Create Risk

Legacy environments are frequently managed by managed service providers (MSPs) that supported the physician practice prior to the acquisition. While those vendors may continue providing services post‑closing, responsibility for security is often poorly defined.

Common pitfalls include:

• Assumptions (or even contractual provisions) that the MSP is responsible for “security” without specifying the specific services or controls the MSP will manage
• Unclear ownership of endpoint protection, firewall management or identity governance
• No formalized escalation or incident response coordination with the health system
• Limited contractual visibility into how the vendor will manage the network or handle privileged access, its responsibilities for implementing specific controls or its liability in the event of a security incident

When a security incident occurs, these gaps matter. Health systems can find themselves accountable for breaches impacting systems they did not design, tools they do not manage and users they do not fully control.

Ambiguous contractual language often complicates accountability for breaches and notification obligations. Many MSPs make ambitious promises when pursuing physician practices as customers yet adopt a minimal role when security incidents arise. To mitigate risk in legacy environments, it is essential to establish explicit security responsibilities, define liability for failures and clarify breach response requirements. Still, health systems acquiring these networks may be reluctant to invest in improvements for infrastructure destined to be decommissioned – underscoring the importance of migrating and shutting down legacy systems swiftly.

Risk Management During the Transition Period

Acquisition does not eliminate risk – it changes who bears it. Until migration is complete, health systems should treat legacy networks as active, high‑risk environments requiring deliberate governance and oversight and – where a third-party IT vendor is involved – clearly defined contractual responsibilities and liability.

Effective risk management during this period includes:

• Treating the legacy network as its own risk domain, not an extension of the enterprise
• Clearly documenting who is responsible for each security control (monitoring, patching, access, backups)
• Reviewing and limiting administrative and service account access
• Implementing segmentation or isolation from the core enterprise network
• Ensuring that logging, alerting and incident reporting align with system‑wide standards

Even where a third‑party IT vendor remains involved, the health system must maintain visibility and understand accountability.

Why Speed Matters: Migrate and Decommission Quickly

The longer a legacy environment remains operational, the longer it remains vulnerable. Every additional day increases the risk that outdated configurations, unpatched systems or compromised credentials will be exploited.

Health systems often delay migration due to operational complexity, EHR transitions or resource constraints, but prolonged coexistence is a risk in and of itself. A defined migration road map should be established as early as possible, with clear timelines for:

• Data and application transition
• Identity and access consolidation
• Decommissioning of legacy infrastructure
• Termination or restructuring of third‑party IT access

The goal is not simply integration – it is risk reduction. Legacy networks should exist only as long as absolutely necessary and no longer.

A Strategic Opportunity, Not Just a Technical Challenge

While IT integration can feel like a post‑closing afterthought, it is increasingly a core component of healthcare risk management. Legacy networks are not just technical debt; they are legal, regulatory and reputational exposure.

Health systems that proactively manage legacy environments – by clearly allocating security responsibility, actively mitigating risk during transition and prioritizing rapid migration – are far better positioned to reduce breach risk and demonstrate diligence to regulators, insurers and patients.