What Is a Penetration Test: A Simple Guide

Kasib Tahir
4 hours ago
7 min read

In 2025, cybersecurity remains more critical than ever: recent reports show that 81% of organisations rate cybersecurity as a high priority. With global cybersecurity spending projected to grow substantially, businesses can’t afford to ignore the risks.

In this guide, we’ll explore:

What a penetration test is
Why a penetration test is important
Who needs a penetration test
What a penetration test covers
The different types of pen tests
How to prepare for a penetration test

We’ll also touch on how to select a good provider of cyber security services (especially those offering penetration testing services) and what to look for when engaging a penetration testing company.

What is a penetration test?

A penetration test (often shortened to “pen test”) is a controlled, ethical simulation of how an attacker might exploit the vulnerabilities in your cyber environments. Rather than just scanning for vulnerabilities (as in a typical vulnerability assessment), a pen test goes further.

It is when a human tester will actively attempt to exploit those vulnerabilities to gain access to critical systems, escalate privileges, move laterally, and ultimately demonstrate how far a real-world threat actor could get.

It’s part of a wider set of cyber security services, but with a specific emphasis on exploitation. You’re essentially asking “if someone tries this, how bad could it get?”.

In a successful penetration test:

The tester identifies weaknesses.
They safely exploit them (in a controlled environment) to show how access might be gained.
They provide insights into what an actual attacker might do.
They deliver actionable remediation advice.

Because of this, a penetration test is a key tool in cyber security assessment services and one of the core offerings of many cyber security companies and penetration testing companies.

Why is a penetration test important?

Below are the major reasons why conducting a penetration test matters. Each reason is crucial to an effective cyber security audit or cyber security management services programme.

Risk identification & prioritisation

By performing a penetration test, organisations can identify their high-risk vulnerabilities so they can prioritise their remediation activities. Simply knowing a system is “out‐of‐date” isn’t enough, a pen test shows whether an attacker could move from that system to your crown-jewels, whether data could be extracted, or whether a foothold could lead to a full breach.

That kind of insight helps risk-based decisions: allowing you apply your cyber security budget and effort where it matters most.

Meet standards & compliance

Many regulatory frameworks (for example, PCI DSS, ISO/IEC 27001) and compliance regimes expect you to demonstrate that your cyber security services include real-world testing and effective control implementation.

Demonstrate mature security culture

Engaging in regular penetration testing demonstrates a mature security culture within the business. It shows stakeholders that you take a proactive approach to security and sends a message that cyber security management services are taken seriously.

Data security & client confidence

For companies that handle sensitive data, a pen test shows that data protection is important. You can show your clients or partners that you took steps to test infrastructure, applications, and external attack surface, and that you didn’t rely only on automated scans. This builds trust and supports your cyber security assessment services offering.

Infrastructure & attack surface assurance

Modern business infrastructures are complex: they can include external systems, cloud, mobile, endpoints, networks, wireless, IoT, internal systems and more. A well-conducted penetration test service helps you test the backbone of your business, from firewalls to domain controllers, connected devices to web applications.

You’re looking at how all these pieces work together, how data flows, who can access what, how systems integrate and whether one small misconfiguration could open the door to a major breach.

Who needs a penetration test?

Penetration testing isn’t just for big enterprises, but some organisations have a stronger case for it. If you fall into any of the categories below, you should seriously consider engaging a penetration testing company or at least reviewing your options for penetration testing services.

Industries with strict regulations: Financial services, healthcare, payment processors, critical infrastructure, government-contractors. These often face compliance standards that require network penetration testing and other pen testing.
Businesses that handle sensitive data: If you store or process customer personal data or business-critical information, you need robust testing.
Organisations making significant changes: If you’re launching a new application, migrating to cloud, redesigning infrastructure, or undergoing digital transformation, you’re changing your attack surface, and so a penetration test helps validate it.
Companies with a large attack surface: If you have many external facing systems, cloud services, mobile apps, APIs, remote workers, IoT devices, wireless networks etc, there are more potential entry points for attack. Pen testing helps map how these combine.
Government and public sector bodies: These are often high-value targets, required to show strong cyber security assessment services and cyber security management services. Penetration testing is a key part.

What can you perform a penetration test on?

When engaging a reputable penetration testing company offering top-tier penetration testing services, testing can cover a wide range of areas, including:

Infrastructure: Tests the backbone of your business such as firewalls, domain controllers, network devices, servers, and connected systems, to ensure strong foundations.
External Infrastructure: Simulates real-world attacks from outside the network to reveal weaknesses an attacker could exploit.
Wireless Assessment: Evaluates Wi-Fi security to uncover weaknesses that could allow unauthorised access.
Active Directory Assessment: Reviews Active Directory environments to uncover weaknesses that could lead to unauthorised access or privilege escalation.
Build Review: Examines system builds and images to ensure secure configurations and reduce the risk of exploitation.
Internal Infrastructure: Tests internal systems to assess how securely they protect critical data once inside the network.
Segmentation Testing: Verifies whether network zones are properly isolated or if one breach could lead to wider access.
Breakout Testing: Assesses restricted systems such as kiosks or locked-down desktops to see if users or attackers can escape into internal networks.
Mobile Applications: Reviews iOS and Android apps to ensure secure design and protect user data.
Desktop Applications: Assesses desktop software to confirm strong security controls and prevent data exposure.
Web Applications: Tests websites and online services to identify weaknesses that automated tools may overlook.
APIs: Evaluates API endpoints to ensure secure communication and prevent unauthorised access.
Cloud Environments: Tests cloud platforms to confirm that security controls and permissions are properly configured.

Additional penetration testing services may include:

Framework alignment with CREST, NIST, OWASP, PCI-DSS, and other standards.
Secure client portals for centralised access to reports, risk scores, and remediation progress.

What are the different types of penetration tests?

Different types of tests suit different objectives. Here’s a breakdown of both the traditional white/black/grey box tests..

White box testing

White box testing involves full knowledge of the system by the tester (source code access, network diagrams, credentials, architecture). Because the tester knows what they’re looking at, it can be very comprehensive and efficient. It’s suitable when you want deep assurance and fewer unknowns.

Black box testing

Black box testing gives the tester little or no knowledge in advance, like a real attacker with no insider info. This simulates an external attack scenario, providing insight into what someone with minimal access could achieve.

Grey box testing

Grey box testing is a hybrid: the tester has some knowledge (e.g., credentials, network layout) and not full access. It reflects a scenario where an attacker has gained some foothold or insider access. It helps test internal attack paths and escalation possibilities.

What are the stages of a penetration test?

A typical penetration test service by a reputable penetration testing company, will follow these stages:

Planning & scoping: Define objectives, systems in scope, rules of engagement, deliverables, legal/contractual terms.
Reconnaissance & information gathering: External scanning, footprinting, identifying assets, gathering intelligence.
Vulnerability assessment: Automated and manual checking for known weaknesses, mis-configurations, open services.
Exploitation: The human tester attempts to exploit vulnerabilities, escalate privileges, pivot, gain access to critical systems.
Post-exploitation & lateral movement: Determine what an attacker could do once inside: escalate privileges, access more systems, extract data.
Reporting: Detailed findings, exploitation path, risk ratings, remediation recommendations tailored for both technical teams and executives.
Remediation & re-testing (optional): After fixes are applied, testers re-test to confirm vulnerabilities are closed and no new ones introduced.

How to prepare for a pentest

If you’re preparing for a penetration test (network penetration testing, web application pen testing, or full pen testing services), here’s how to get ready:

Define the scope clearly: which assets, applications, networks, cloud environments are included?
Set objectives: what are you trying to test? External attack surface? Internal lateral movement? Cloud mis-configs? What are your pen testing goals?
Choose the right type of test: (white/black/grey box).
Ensure internal stakeholders (IT, security operations, business owners) are aware: set expectations for potential disruption, scheduling.
Verify legal & contractual boundaries: ensure testers have permission, ensure no surprise outages.
Provide documentation where helpful: network diagrams, architecture info (especially for white box or grey box).
Ensure you have remediation processes ready: receiving the report is only the start, you’ll need to act on it.
Communicate to business management: allocate budget and resources for remediation. A pen test isn’t useful if you just file the report and forget it.
After completion, schedule a review session: understand findings, prioritisation, who will fix what and by when.
Consider integrating the pen test into your ongoing cyber security management services and vulnerability management programme, so it’s part of a continuous improvement cycle.

Pen Test FAQ

How often should we do a penetration test?

Many organisations perform them annually, or after significant changes (new applications, infrastructure migrations). For high-risk environments, more frequent testing may be warranted.

What’s the difference between a vulnerability assessment and a penetration test?

A vulnerability assessment focuses on finding and listing known vulnerabilities (scans, automated checks). A penetration test goes deeper: it attempts to exploit vulnerabilities, emulate attacker actions, and see how far someone could go.

Will the penetration test disrupt our operations?

It can, but a reputable penetration testing company will plan carefully, define rules of engagement, schedule during low-impact windows, and avoid production outages. You should clarify this in advance.

What do we get from a penetration test report?

You’ll get a detailed breakdown of findings: exploitation paths, systems accessed, data that could be compromised, risk ratings, remediation advice. Often this is tailored for technical teams and for executive/board summaries. At One Compliance, we provided technical and non-technical reports so information is accessible for all people across the business.

How do we select a good penetration testing service or penetration testing company?

Look for credentials (industry-recognised certifications), experience across your environments (cloud, apps, infrastructure), clear methodology (aligned with frameworks like CREST, NIST, OWASP), good reporting, ability to integrate with your cyber security assessment services and cyber security managed services.

Why choose One Compliance for your pen test

At One Compliance, we combine technical rigour with actionable insight to help you reduce risk meaningfully.

Our approach:

We assess infrastructure, networks, web and mobile applications, cloud, containers and more.
We follow recognised frameworks (CREST, NIST, OWASP, PCI-DSS) to ensure our work aligns with global best practices.
We deliver clear, executive-friendly reports plus technical findings for your teams.
We integrate findings into your broader cyber security audit and cyber security management services, so pen testing isn’t a one-off but part of continuous improvement.

Contact One Compliance today to discuss your pen testing requirements and schedule your penetration test service. Safeguard your business, protect your data, and strengthen your security posture with a trusted penetration testing company who understands your world.