With security software evolving quickly to mitigate growing threats, many organisations now face problems with legacy software. This blog outlines the risks of legacy software and also explains why organisations need regular security updates and audits to maintain a strong security posture.

What is Legacy Software?

Legacy software, also known as older software, operating systems, or infrastructure, is still in use despite being outdated. Organisations typically rely on these tools because they support historic key business processes. They also link closely to other systems, meaning replacing them would be costly and time-consuming.

With this in mind, it’s no wonder many businesses opt to stick with applications they are familiar with, regardless of whether they are outdated and at risk of cyber threats.

What Makes Software “Legacy”?

Software is typically considered legacy when it has one or more of the following traits:

No longer supported by the vendor: When software is no longer supported by the provider, that also means no bug patches, updates, or security fixes.

Built on outdated technology: Software built on outdated technology is hard to maintain or integrate with modern software, which disrupts operations and wastes employees’ time.

Requires specialised knowledge: In many organisations, people need specialised knowledge to use software optimally. Often, only a few employees or contractors with a lot of software experience will know this. New hires likely won’t receive training on it, which increases risk due to insufficient training.

Depends on older hardware or operating systems: Relying on old hardware that is also nearing end-of-life is a critical issue that characterises much legacy software.

Has limited documentation: Limited documentation makes changes risky and slow. It also makes incident response complex.

Why do companies still use legacy software?

Despite the security vulnerabilities, legacy systems often remain in place because:

• They run mission-critical operations (finance, manufacturing, healthcare, logistics, etc.)
• Replacement could cause downtime or operational disruption for businesses, impacting income.
• Migration projects can be expensive, especially when data and integrations are complex.
• The software may have been custom-built and tailored to unique workflows.

It’s no surprise, then, that many businesses stick with what they know. They avoid safer options that require a period of operational change.

The cybersecurity risk behind legacy software

The biggest issue is simple: older software is easier to attack.

When a system stops receiving security updates, any newly discovered vulnerabilities remain open forever. Attackers actively search for these weak points, especially in industries known for running long-standing systems like healthcare.

In the next section, we’ll break down the most common cybersecurity threats tied to legacy devices and how to reduce the risk without affecting business operations.

The most common cybersecurity risks to be aware of

Legacy technology brings a unique range of risks to an organisation. This is true, no matter how skilled your security team is. Here are some of the most common cyber risks introduced by older systems to be aware of:

• Unpatched vulnerabilities: Vendors stop releasing security updates for end-of-life systems, leaving known exploits permanently exposed to attackers.
• Lack of vendor support: Without ongoing support, there’s no one to turn to for fixes when new threats or bugs emerge.
• Incompatibility with modern security tools: Legacy systems often can’t run current endpoint detection tools, encryption standards, or multi-factor authentication. This creates blind spots in defences.
• Weak or outdated authentication: Older systems frequently rely on deprecated protocols and weak password policies, with no support for modern MFA.
• Poor logging and visibility: Older systems often lack audit trails and monitoring. This makes threat detection and incident response harder.
• Increased attack surface: Outdated systems often stay online “just in case.” This quietly increases the number of entry points for attackers.
• Risky integrations with modern systems: Connecting legacy tech to current networks via bolt-on integrations or middleware can introduce new, poorly understood vulnerabilities.
• Compliance gaps: Legacy systems often can’t meet current regulatory requirements (such as GDPR or PCI-DSS), risking both fines and breaches.
• Single points of failure: Critical legacy systems are often maintained by just one person or team, leaving institutional knowledge undocumented and creating a single point of failure.
• Costly, disruptive remediation: The longer legacy technology stays in place, the harder and more expensive it becomes to replace or patch without causing downtime.
• **Shadow IT workarounds:** Staff frustrated by clunky legacy systems may use unsanctioned tools or processes. This creates extra risk that security teams may not see.

How can I effectively begin replacing legacy systems?

Replacing legacy systems is not a one-size-fits-all solution for businesses. Some businesses need more fixes than others. Organisations with stricter rules, like fintech and healthcare, should focus more on replacing legacy systems to help protect customer data and reduce security risk.

However, there are some recommended steps any organisation can take to begin effectively replacing outdated software. Here are our expert recommendations for strengthening an organisational security strategy and replacing any legacy systems with minimal disruptions to day-to-day operations.

• Audit and inventory systems: Identify every legacy system in use, map dependencies between them, and assess which pose the greatest security or compliance risk to prioritise first.
• Risk-rank before replacement: Focus on systems handling sensitive data or critical operations first, rather than tackling all legacy applications at once.
• Plan a phased migration: Replace or upgrade systems incrementally, running parallel environments where needed, to avoid disrupting day-to-day operations.
• Build in staff training and change management. Train teams on new systems early. Provide clear support, so adoption is smooth. Prevent old workarounds from returning.

Making employees comfortable with new user interfaces is key in reducing any risk of a data breach during this transition period to new operating systems.

How can I ensure my transition is cost-effective?

Any organisation’s board is likely going to be conscious of the cost of any transition from legacy software to new software. Communicating the value of investing in new, safe tools is essential in winning over your board and demonstrating that the maintenance cost of any new software far outweighs the potential risks of remediation costs for a data breach.

Frame the cost comparison clearly: Weigh the ongoing cost of maintaining legacy systems against the average cost of a data breach in your sector, including fines, incident response, and reputational damage.

Prioritise based on risk, not sentiment: Use risk-ranking to sequence spend, tackling the highest-risk systems first and phasing the rest over a realistic timeline.

Factor in the full cost of “doing nothing.”: Legacy systems bring rising costs over time.

These include support contracts, specialist staff, and inefficiencies. Over time, these costs add up. Inaction often becomes the more expensive long-term option.

Look for consolidation opportunities: Replacing multiple systems at once can reduce licences, vendors, and support contracts, adding savings alongside the security case.

Consider phased or cloud-based options. Subscription models can lower upfront costs. They spread spending over time, making budgeting more predictable.

Tie investment to business outcomes: Link the new system to efficiency, customer experience, and competitive advantage. This can widen the board’s reasons to invest.

How OnSecurity can help in overcoming legacy software risks

OnSecurity’s platform-led offensive security services support organisations in overcoming legacy software risks through a thorough investigation of your existing software and any possible vulnerabilities it may introduce.

Our expert-led website penetration testing identifies exploitable weaknesses in outdated systems before attackers do, giving you clear, prioritised visibility into where legacy technology poses the greatest risk. Our platform shows findings in real time, with actionable remediation guidance, so your team can focus resources where they matter most.

With ongoing testing cycles, we help you track risk as you mitigate and catch vulnerabilities early. Moving away from legacy systems strengthens an organisation’s security posture at every stage, not just at the end.