A penetration test, colloquially known as a pentest or ethical hacking, is an authorized simulated cyberattack on a computer system, performed to evaluate the security of the system; this is not to be confused with a vulnerability assessment. The test is performed to identify weaknesses (also referred to as vulnerabilities), including the potential for unauthorized parties to gain access to the system's features and data, as well as strengths, enabling a full risk assessment to be completed.

The process typically identifies the target systems and a particular goal, then reviews available information and undertakes various means to attain that goal. A penetration test target may be a white box (about which background and system information are provided in advance to the tester) or a black box (about which only basic information—if any—other than the company name is provided). A gray box penetration test is a combination of the two (where limited knowledge of the target is shared with the auditor). A penetration test can help identify a system's vulnerabilities to attack and estimate how vulnerable it is.

Security issues that the penetration test uncovers should be reported to the system owner. Penetration test reports may also assess potential impacts to the organization and suggest countermeasures to reduce the risk.

The UK National Cyber Security Center describes penetration testing as: "A method for gaining assurance in the security of an IT system by attempting to breach some or all of that system's security, using the same tools and techniques as an adversary might."

The goals of a penetration test vary depending on the type of approved activity for any given engagement, with the primary goal focused on finding vulnerabilities that could be exploited by a nefarious actor, and informing the client of those vulnerabilities along with recommended mitigation strategies.

Penetration tests are a component of a full security audit. For example, the Payment Card Industry Data Security Standard requires penetration testing on a regular schedule, and after system changes. Penetration testing also can support risk assessments as outlined in the NIST Risk Management Framework SP 800-53.

Several standard frameworks and methodologies exist for conducting penetration tests. These include the Open Source Security Testing Methodology Manual (OSSTMM), the Penetration Testing Execution Standard (PTES), the NIST Special Publication 800-115, the Information System Security Assessment Framework (ISSAF) and the OWASP Testing Guide. CREST, a not for profit professional body for the technical cyber security industry, provides its CREST Defensible Penetration Test standard that provides the industry with guidance for commercially reasonable assurance activity when carrying out penetration tests.

Flaw hypothesis methodology is a systems analysis and penetration prediction technique where a list of hypothesized flaws in a software system are compiled through analysis of the specifications and documentation for the system. The list of hypothesized flaws is then prioritized on the basis of the estimated probability that a flaw actually exists, and on the ease of exploiting it to the extent of control or compromise. The prioritized list is used to direct the actual testing of the system.

There are different types of penetration testing, depending upon the goal of the organization which include: Network (external and internal), Wireless, Web Application, Social Engineering, and Remediation Verification.