What Is Penetration Testing? A Plain-English Guide

Every business has security weaknesses. The question is whether you find them first — or an attacker does.

Penetration testing (also called pen testing or ethical hacking) is how you find out. A security professional — one you authorise and hire — attempts to break into your systems using the same techniques a real attacker would use. The difference: they hand you a detailed report instead of stealing your data.

This guide explains exactly what penetration testing is, how it works, the types available, and whether your business actually needs it.

What does a pen tester actually do?

A penetration tester uses the same tools, tactics, and techniques as a malicious hacker — but with your knowledge and permission. During a test, they might:

• Try to access systems using stolen, guessed, or phished credentials
• Exploit known vulnerabilities in your software or web applications
• Attempt to intercept unencrypted network traffic
• Send phishing emails to your employees to test awareness
• Look for misconfigurations in cloud environments, firewalls, or servers
• Try to escalate privileges after gaining initial access

The goal isn’t just to find a weakness — it’s to exploit it the same way a real attacker would. That’s what makes a pen test different from a basic vulnerability assessment, which only identifies potential issues without testing whether they can actually be used.

Why do businesses need penetration testing?

Three reasons drive most businesses to book a pen test:

1. Compliance requirements

Many regulatory frameworks — including PCI DSS, ISO 27001, SOC 2, and HIPAA — either require or strongly recommend regular penetration testing. If you process card payments or handle sensitive data, you may not have a choice.

2. Proactive risk reduction

The average cost of a data breach in 2024 was $4.88 million (IBM Cost of a Data Breach Report). A pen test typically costs a fraction of that — and finding a critical vulnerability before attackers do can prevent a breach entirely.

3. Proving security to customers and partners

Enterprise buyers increasingly require vendors to demonstrate security assurance before signing contracts. A recent pen test report — especially from an independent third party — is one of the fastest ways to satisfy that requirement.

How penetration testing works: the 5 phases

Every professional pen test follows a structured methodology. Here’s what happens at each stage:

Phase 1 — Planning

Before anything begins, you and the pen testing provider agree on scope: which systems are in scope, what testing methods are permitted, testing windows (to avoid disrupting production), and rules of engagement. Everything is documented and signed off.

Phase 2 — Reconnaissance

The tester gathers information about your environment — domain names, IP addresses, employee names, technologies used, publicly exposed services. This mirrors exactly what an attacker would do before launching an attack.

Phase 3 — Scanning

Using specialised tools, the tester maps your network: open ports, running services, software versions, and known vulnerabilities. This builds a picture of potential entry points.

Phase 4 — Exploitation

This is the active testing phase. The tester attempts to exploit the vulnerabilities identified — trying to gain access, escalate privileges, move laterally across the network, and reach sensitive data. All activity is logged.

Phase 5 — Reporting

You receive a detailed report covering every vulnerability found, evidence of exploitation, risk ratings, and specific remediation recommendations. Most providers also offer a debrief call to walk through findings.

Types of penetration testing

Not all pen tests are the same. The right type depends on what you’re trying to protect:

What happens after a pen test?

A good pen testing provider doesn’t just hand you a list of vulnerabilities and disappear. After the test, you should receive:

• An executive summary — a non-technical overview of risk for leadership and board-level stakeholders
• A technical findings report — full details of every vulnerability, how it was exploited, and evidence
• Risk ratings — critical, high, medium, low, and informational findings prioritised by impact
• Remediation guidance — specific steps to fix each issue, not just a list of problems
• A debrief call — a walkthrough of findings with your technical team

Once your team has remediated the critical and high findings, many providers offer a re-test to verify the fixes worked.

How often should your business do a pen test?

• Annually as a minimum — for most businesses, one comprehensive test per year is the baseline
• After major changes — a new product launch, cloud migration, or acquisition warrants a targeted test
• Before compliance audits — PCI DSS requires annual pen testing; booking one ahead of your audit gives you time to remediate findings
• Quarterly for high-risk environments — financial services and healthcare organisations often test more frequently

Penetration testing vs vulnerability scanning: what’s the difference?

A vulnerability scan is automated software that checks your systems against a database of known vulnerabilities. It’s fast, relatively cheap, and useful — but it only identifies potential weaknesses without attempting to exploit them.

A penetration test is manual, expert-led, and goes further. A tester doesn’t just flag that a vulnerability exists — they prove it can be exploited, show what data or access could be reached, and demonstrate the business impact.

Think of a vulnerability scan as a checklist and a penetration test as a live fire exercise. See our vulnerability assessment service for more on how the two work together.

If you operate in a regulated industry, penetration testing requirements may be even more specific. See our guides for financial services cybersecurity and healthcare cybersecurity for industry-specific context.

Frequently asked questions

Will a pen test take down our systems?

A professional pen test should not cause downtime. Before testing begins, scope and rules of engagement are agreed — including which systems are off-limits and acceptable testing windows. Most tests are conducted outside business hours to further reduce risk. That said, you should always have a backup and know your incident response contacts before any test.

How much does penetration testing cost?

A typical network or web application pen test runs between $5,000 and $30,000 depending on scope, environment size, and depth of testing. Red team exercises are more involved and can run higher. See our pen testing cost guide for a full breakdown.

Do small businesses need penetration testing?

Yes — and attackers agree. Small businesses are increasingly targeted precisely because they tend to have fewer security controls. If you handle customer data, process payments, or provide services to larger organisations, a pen test is worth considering. Many SMB-focused tests are scoped to keep costs manageable.

What’s the difference between a pen test and a red team exercise?

A penetration test targets specific systems or applications within a defined scope. A red team exercise is a broader, scenario-based simulation of a full attack — covering network, physical access, and social engineering in combination — with no pre-defined scope. Red team engagements are longer, more expensive, and better suited to organisations with a mature security posture already in place.

How do we prepare for a pen test?

You don’t need to clean up your environment first — that defeats the purpose. What you should do: make sure your team knows the test is happening, have a contact list ready in case something unexpected is discovered, and ensure your test provider has signed an NDA and rules of engagement before work begins.