The hidden risks in acquired codebases (and how to uncover them fast)

The first few months after the acquisition are very important. This is the time when you are still learning how everything works. If you miss a serious bug or security issue now, it can cause bigger problems later. Ignoring bad design or outdated code can also lead to slow performance and scaling issues.

The challenge is that most reviews focus only on features and infrastructure. But the biggest risks are often buried deep in the code itself.

In this article, we will discuss the most common hidden risks in acquired codebases and a simple way to identify and fix them early.

Why acquired codebases are riskier than they appear

The problem with inherited code is that it comes with invisible baggage. Unlike your own codebase, where you understand the evolution and trade-offs, an acquired system is a black box built by engineers who made different assumptions, faced different pressures, and may have left the company entirely. Consider these realities:

1. Documentation never tells the whole story. Even good documentation often omits the reasons for certain choices. It also rarely mentions the problems that people already know about but haven’t fixed yet. Most of that knowledge lives in the minds of engineers who might already have left.
2. Technical debt accumulates silently. That working payment system might be held together by a single library that's three major versions behind and has known security vulnerabilities. The API that handles thousands of requests daily might be one database connection away from cascading failure.
3. Culture and practices vary dramatically. The acquired team might have had different standards for testing, code review, security practices, or deployment procedures. These differences aren't just about style; they represent different risk tolerances that are now your responsibility.

The six categories of hidden risk

1. Security vulnerabilities and compliance gaps

Security vulnerabilities in the acquired codebase are even more risky because they often affect systems already running in production. Sometimes acquired codebases lack required compliance, and you may not even know about them.

Important things to check:

• Outdated dependencies: These are the easiest to find and fix. Run a quick dependency check using tools like Synk or Dependabot. You need to pay extra attention to dependencies that are two major versions behind and have known security warnings.
• Authentication and authorization: Check these carefully. Look for any custom-built security code or hardcoded passwords (even inside the comments or docs).
• Compliance: Many teams focus on building features first and address compliance later. This creates a hidden risk in an acquired codebase. Review how personal data (PII) is stored and protected. Are there any clear data retention policies?

Quick audit steps:

• Run automated scans using tools like SonarQube to identify basic issues.
• Manually review the authentication flow to ensure there are no weak spots.
• Scan commit history for secrets using tools like GitGuardia, and treat anything found as compromised.

2. Architectural decisions that don't scale

The codebase might work fine at its current scale, but it contains architectural choices that become expensive problems as usage grows or as you integrate it with your existing systems.

Points to take care of:

Monolithic architectures aren’t inherently bad. They work well until they start blocking independent scaling or deployment of critical components. It’s worth checking if the current structure still fits how your team deploys and scales.

Database design issues are usually cheap to ignore early and expensive to fix later. Take a closer look at the schema. Are queries fast enough? Do the right indices exist? Does the design actually support what you’re building next?

External dependencies can also sneak up on you. If critical components depend on third-party services, that’s a risk.

How to approach an audit:

• Load test under realistic conditions: Simulate expected traffic and identify bottlenecks early
• Analyze database queries: Check slow query logs for problematic patterns
• Document the critical path: Trace key user flows to understand dependencies and single points of failure

3. Testing gaps and quality assurance debt

It is important to go through unit test cases in the acquired codebases. Even if there are tests, don’t trust test coverage numbers alone; they can be misleading.

Points to take care of:

Low test coverage is the obvious indicator, but test quality matters more than quantity. Look at what's actually being tested. Are there integration tests for critical business logic? Do tests cover edge cases and error conditions? Or are they mostly testing trivial getters and setters?

Brittle tests that frequently break without actual bugs indicate poor test design and make developers reluctant to refactor. Check the CI/CD history for any test tasks that are disabled.

If end-to-end testing is missing, that means user flows are not properly validated. Critical workflows might have been working in production solely through workarounds, rather than proper validation.

How to approach an audit:

• Generate coverage report: Use Istanbul, JaCoCo, or Coverage.py to identify untested critical paths
• Review test quality: Read actual tests to ensure they test behavior, not implementation details
• Run tests multiple times: Catch flaky tests that indicate reliability problems

4. Operational and observability blind spots

You can’t fix what you can’t see. Many acquired codebases lack a proper troubleshooting system. The code should have proper monitoring and alerts. Without them, fixing production issues becomes a nightmare.

Points to take care of:

Insufficient logging leaves you blind during incidents. Check whether the system logs meaningful events, includes proper context (request IDs, user IDs, correlation IDs), and uses appropriate log levels. Excessive debug logging in production or critical errors logged only as warnings indicate operational immaturity.

Missing metrics make capacity planning guesswork. If key performance metrics don't exist, you're flying blind.

Quick audit approach:

• Deploy to staging and observe: Run realistic workloads to see what information is available during issues
• Review incident history: Ask about recent problems, discovery methods, and missing information
• Check runbook completeness: Verify documented procedures exist for deployments, rollbacks, and incident response

5. Knowledge transfer gaps and documentation debt

The people who created the system understand it deeply. But the knowledge is often not readily available. Especially when acquisitions happen, people leave, and the undocumented knowledge is also gone with them.

Points to take care of:

Outdated documentation is common. It becomes a real problem in complex systems. If the docs were last updated a year ago, they’re likely not accurate. You may find logic or calculations that no one has explained. Without notes on design decisions, it’s hard to understand why something was built that way.

Quick audit approach:

• Conduct immediate knowledge transfer: Schedule dedicated sessions with the original team and record them
• Identify bus factor for each component: Find areas only one person understands and prioritize documentation
• Create a living architectural document: Start with high-level diagrams and evolve as you learn more

6. Technical debt and code quality issues

All codebases have technical debt, but inherited systems often have debt you didn't consciously choose. Understanding the type and severity of debt helps you plan refactoring efforts and avoid worsening it.

What to look for:

Code duplication is a sign of rushed work. It also shows poor coordination among developers. Duplicated business logic is a bigger problem. A single bug fix must be repeated in many places. If one copy is missed, it can lead to hidden bugs.

Tight coupling between components makes changes expensive and risky. Look for modules that import from many other modules, classes with excessive dependencies, or business logic embedded in presentation layers.

Inconsistent coding patterns indicate multiple development eras or insufficient code review. When the codebase looks like it was written by five different teams (because it was), maintenance becomes harder as developers context-switch between different styles and patterns.

Quick audit approach:

• Run code quality tools: Use tools like SonarQube or linters to identify complexity hotspots automatically
• Identify messiest areas: Visualize code complexity and churn; prioritize files that are both complex and frequently modified.
• Measure change difficulty: Estimate effort for realistic features to identify coupling problems

Building your 30-day audit plan

During acquisitions, things move fast. You won’t have time to check everything deeply. Focus on what matters most first.

Week 1: Automated discovery and quick wins

Begin with automation. Run all tests, including security scanners and dependency checkers. Also, run the unit tests to identify test coverage.

Set up basic monitoring. Add performance tracking to see how the system behaves. Add error tracking to capture issues as they happen. You need clear visibility before you make any changes. Document all external dependencies. This helps you understand what is within your control and what is not.

Week 2: Critical path analysis

Trace the top five user flows through the system. You can focus on business-critical operations first. Document how they work and what could break.

Review authentication and payment processing thoroughly. These are too important to leave to later. Any issues here need immediate attention.

Interview the original team about known issues. They know all the undocumented issues. Create a prioritized list of known problems and their corresponding impacts.

Week 3: Architecture and integration planning

Assess integration points with your existing systems. How will this codebase fit into your infrastructure? What needs to change to enable that integration?

Evaluate the deployment pipeline. How does code currently get to production? What needs to be changed to match your organization’s standards?

List the biggest tech debts and estimate the effort required to clean them up. This helps in creating a plan to adapt the codebase to your organization’s setup.

Week 4: Documentation and team readiness

Create documentation for critical operations. Your team needs to run daily operations independently.

Also, document the current architecture with technical details. This becomes the base for future development.

You can follow a 90-day technical roadmap. This would prioritize the security fixes and any dependencies with the current team. Be realistic about capacity.

Making the go or no-go decision

In reality, the acquisitions are done to benefit the business. The technical challenges are a side effect of it. Your audit should give you enough information needed to make the final call.

Green flags that suggest a healthy codebase:

Active maintenance is evident from recent commits, updated dependencies, and resolved issues. The team was investing in the system's future, not just keeping it running.

Good test coverage, along with meaningful tests, indicates quality-conscious development. Tests serve as documentation of expected behavior and make changes safer.

Clear architecture with documented decisions shows thoughtful design. They make it much easier to adapt to the new standard.

Red flags that suggest serious problems:

Pervasive security vulnerabilities across multiple categories indicate systemic issues with development practices. Fixing individual vulnerabilities is not enough. You also need to fix the culture that created these vulnerabilities.

If the shared code doesn't work locally, it means your team can't work productively on it. If the original team needed special knowledge or access to make changes, you'll have that problem too.

Critical dependencies on individuals rather than documentation mean knowledge loss is imminent. If only one person can deploy to production or knows how a critical component works, you're one resignation away from crisis.

Conclusion

Acquiring a codebase means acquiring both assets and liabilities. The difference between success and an expensive mistake comes down to how quickly you identify the hidden risks.

Your first month sets the direction. Start by moving fast so you can see how things actually work. As you explore, you’ll notice where the biggest risks are. Once you see the patterns, take time to understand the system deeply. With that clarity, build a plan that turns the system into something valuable.

Start your audit today. The risks aren't getting smaller while you wait.