How to Assess Legacy Software: Detailed Guide

5 min readFeb 16


Using outdated technology can be expensive. According to Kaspersky’s IT Security Economics 2020, it costs as much as $1.225 million per year for individual enterprise companies in the USA. In the UK on the other hand, the government spends north of £2.3 billion to keep outdated systems working.

As more and more businesses embrace digital transformation, the need to keep track of different software versions and where necessary, modernize them so that they meet the user experience and security demands of today is very important.

This is especially true for so-called “legacy software”: software that was created for older system architecture.

This guide will provide an overview of how to assess legacy software including the steps and best practices involved.

What is the Assessment of Legacy Software?

The assessment of legacy software is the process of auditing and analyzing an existing software system that is no longer actively developed or supported, or has been outgrown by the company.

The goal of this process is to identify any technical debt or potential risks associated with the continued use of the system, as well as to determine whether it should be maintained, replaced, or retired. This is the first mandatory step for any company thinking about modernizing its legacy software.

Testing legacy software will answer the following questions:

  • Is the software still supported by the vendor?
  • Is the software stable and running smoothly?
  • Are there any known security vulnerabilities?

In many industries, legacy software is widespread. They include:

  • Financial Services
  • Healthcare
  • Manufacturing
  • Energy & Utilities
  • Government Agencies

Evaluating the systems used in these industries is essential for staying competitive and avoiding costly disruptions.

Why You Need to Assess Legacy Software

There are several reasons why you should assess legacy software. This process is vital if you are thinking about:

  • Adding new features
  • Ensuring compliance with current industry standards and regulations
  • Improving your company’s competitive advantage
  • Identifying areas that may need to be updated or replaced
  • Reducing risk
  • Identifying and resolving bugs
  • Increasing performance

There are potential risks associated with not implementing a legacy software assessment.

  • Security vulnerabilities or other critical issues
  • Decreased performance
  • Inability to add new features and functionality that could be beneficial to your business
  • Non-compliance with industry standards and regulations
  • Legal and financial consequences

By taking the time to know how to identify a legacy system and assess it, you can ensure that your solution will still be able to meet your needs into the future. Better still, you can know when it is time to modernize it so it meets with current trends and technologies.

5 Steps to Assessing a Legacy Software

When it comes to deciding between continuing to support and maintain a piece of software or modernizing it, there are a few key stages that need to be considered.

So, how are legacy systems assessed? The typical steps are:

1. Legacy code review

This is an overview of the code base, designed to identify areas where the code is no longer maintainable or supportable. This will give you a better understanding of how it works and if it’s up to current coding standards.

To get a head start on your legacy software review, sign up for our free code assessment and quickly identify areas where you need improvements.

2. Functionality audit

This audit is designed to determine whether or not the legacy software is able to support the arising business needs and challenges. This includes testing the system to ensure that it performs as intended, and identifying any areas for improvement or issues. Or simply if the software brings any value to business now.

3. Compliance audit

If you’re subject to any industry or government regulations, you’ll need to make sure that your software is compliant, especially legacy one. This audit will help you identify any areas that need to be addressed, as well as any new compliance requirements that have arisen since the software was last updated.

The software can also be checked for compliance with regional or global security standards.

  1. List all legacy software in the organization.
  2. Identify all software with a high level of security risk
  3. Assess the risks identified in step 3.
  4. Determine the most effective ways to mitigate these security threats
  5. Calculate the Total Cost of Ownership (TCO)

4. Security audit

This audit will help you identify any security risks and what needs to be done to mitigate them. Penetration testing can be used, for example, to identify vulnerabilities in the outdated operating system.

I + M — R = TCO

  • I — Initial cost.
  • M — Maintenance/ operations cost over the software’s lifespan.
  • R — Possible Resale Value.

Also, a Risk Management Framework, or RMF, can provide a framework for carrying out a security audit to determine the risks associated with legacy software. RMF works by establishing the business’ objectives, identifying technical risks associated with the legacy application, and determining their impact on the organization.

RMFs typically include the following steps.

Finally, you’ll need to calculate the total cost of ownership (TCO) for the legacy software. This will take into account license fees, maintenance costs, and support costs, as well as any necessary updates, upgrades, and migrations.

TCO can be calculated as:

The goal here is to determine whether continuing to use or replacing the system is cost-effective for the organization.

A change in your technology landscape can be a significant challenge, but ModLogix can help. Get in touch to discuss your goals.

Challenges of the Legacy System Assessment

There are several common challenges that organizations face when testing legacy code, including:

Documentation can be scarce and/or outdated

One of the first challenges you’ll face when assessing a legacy system is a lack of documentation. Over the years, documentation can simply disappear. Even when you find the documentation, it can be outdated and misleading, as it may not reflect the current state of the software.

Large monolithic applications are difficult to comprehend

Another challenge with legacy software is that it can be very difficult to understand. Large, monolithic applications can be complex and confusing. And when you can identify and isolate issues, it may be difficult to implement changes without introducing new problems.

Requires a lot of time and effort

Testing a legacy system can be a time-consuming and labor-intensive process. It can take weeks or even months to fully understand an application. And, once you have a clear understanding of the application, you still have to identify any issues and make recommendations.

Automated testing may not be possible

Automated testing is a vital part of the software development process. It helps identify errors and potential problems early in the development cycle. However, automated testing may not be possible when evaluating legacy software. This means it is difficult to perform regression testing and to ensure that changes do not introduce new issues.

Disruption of business-critical processes

When you test legacy software, changes may have to be made to the software or how it is used, which can disrupt business-critical processes. This can cause downtime or business disruptions.

To avoid this, a phased approach is best. Adopt agile methodology when doing your assessments and manage the process in small incremental phases or chunks.

Read the full article on ModLogix.

Originally published at on February 16, 2023.




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