What is a Penetration Test and Does Your Business Need One?

A penetration test — commonly called a pentest — is an authorised, simulated attack on your systems, networks, or applications, carried out by security professionals with the explicit goal of finding weaknesses before a real attacker does. It is, in effect, hiring someone to try to break into your business so you know exactly where you are exposed.

The word “authorised” matters here. Everything that distinguishes a penetration tester from a criminal is the written agreement that defines scope, timing, and rules of engagement before any testing begins.

Penetration Testing vs Vulnerability Scanning

These terms are often used interchangeably, but they describe very different things.

A vulnerability scan is an automated process. Software runs against your systems, compares what it finds against a database of known weaknesses, and produces a list. It is fast, repeatable, and useful — but it is not a pentest. It cannot chain vulnerabilities together, exploit human behaviour, or discover issues that do not match a known signature.

A penetration test involves skilled humans. A tester takes the output of automated scanning as a starting point, then applies judgement, creativity, and technical expertise to determine which vulnerabilities are actually exploitable, how they could be combined, and what an attacker could realistically achieve. A finding rated “medium” by a scanner might turn out to be critical when a tester demonstrates it provides access to your payroll data.

Types of Penetration Test

Network penetration testing examines your internal and external network infrastructure — firewalls, routers, servers, and the services they expose. External tests simulate an attacker on the internet; internal tests simulate an attacker already inside your network (a disgruntled employee or a compromised device).

Web application testing focuses on websites, web apps, and APIs. It looks for issues such as SQL injection, broken authentication, insecure direct object references, and exposed sensitive data — the vulnerabilities most commonly exploited in data breaches.

Social engineering tests your people rather than your systems. This might involve phishing simulations, phone-based pretexting calls, or — in physical tests — attempts to gain unauthorised building access.

Physical penetration testing is less common but relevant for businesses where physical security matters: server rooms, office access controls, clean-desk policy, and whether a visitor could walk out with sensitive equipment.

What the Process Looks Like

Scoping comes first. You and the tester agree on what will be tested, what is out of bounds, the testing window, and the rules of engagement. This stage also establishes the “knowledge level”: black box (the tester starts with no information, simulating an external attacker), grey box (partial information, simulating a semi-insider), or white box (full access to documentation and code, maximising coverage).

Testing follows. Depending on scope, this can take anywhere from a day to several weeks. Good testers communicate throughout — particularly if they discover something critical that needs immediate attention.

Reporting is where the value is delivered. A quality report includes an executive summary suitable for non-technical stakeholders, a detailed technical section with each finding, its severity, and reproducible evidence, and — crucially — clear remediation guidance prioritised by risk.

Remediation and retesting complete the cycle. Fixing vulnerabilities without confirming the fix worked is a common mistake. Most reputable testers offer a retest of critical and high findings to verify that remediation was effective.

How Often Should You Test?

Annual testing is a reasonable baseline for most small businesses. More frequent testing makes sense after significant changes: launching a new application, moving infrastructure, acquiring another company, or after a security incident. Regulated industries and businesses handling payment card data or healthcare records often have mandatory testing requirements.

Who Needs a Penetration Test?

Any business that holds customer data, processes payments, or maintains an online presence has attack surface that warrants professional assessment. If a breach would damage your reputation, trigger regulatory fines, or interrupt revenue, you have reasons to test.

Penetration testing is also increasingly requested by enterprise clients during procurement. If you want to win contracts with larger organisations, a recent test report is often a requirement.

What Does It Cost?

Costs vary significantly based on scope and tester experience. As a rough guide:

• A basic external network test for a small business: £1,500–£4,000
• A web application test: £2,000–£6,000
• A combined network and application test with social engineering: £5,000–£15,000

These figures represent professional, accredited UK testers. Cheaper offerings exist, but the quality of finding and reporting varies enormously. Look for testers holding CREST accreditation or CHECK status for government work, and individuals with OSCP, CEH, or similar certifications.

What to Do with the Results

A pentest report is only useful if it drives action. Prioritise critical and high findings first. Assign remediation ownership internally. Set deadlines. Schedule a retest. Share the executive summary with your board or senior leadership — security investment decisions require visibility of actual risk, and a report provides the clearest evidence available.