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Commerce Security Authority
Category: Incident Response and Skimming

Forensic Evidence

Also known as: forensic material, scientific evidence
Simply put

Forensic evidence is material collected and examined using scientific methods to help investigate whether a crime has occurred and to support findings that may be presented in a court of law. It is gathered during legal searches or from crime scenes and analyzed by trained specialists. In a payment security context, this concept underlies the investigative process used to establish what happened during a suspected breach or fraud incident.

Formal definition

Forensic evidence refers to material collected during a legal search or from a scene and examined through scientific methods and expertise to investigate crimes or to be presented in a court of law. It encompasses items analyzed by forensic scientists to help establish whether a crime has taken place, using methods such as biological, chemical, and analytical testing described in the general forensic science literature. As presented in the evidence packet, the term is defined at a general legal and scientific level; its application to specific domains such as payment card breach investigation depends on the applicable investigative standards, chain-of-custody controls, and jurisdictional rules, which are out of scope for this general definition and should be confirmed against the relevant published requirements.

Why it matters

Forensic evidence is the foundation of any credible investigation into whether a crime has occurred. Because it is collected through legal searches or from a scene and examined using scientific methods and expertise, it can be presented in a court of law to help establish what happened. In a payment security context, this same investigative discipline underlies how a suspected breach or fraud incident is examined: findings are only as reliable as the methods used to gather and analyze the underlying material.

The integrity of forensic evidence matters because conclusions drawn from it may carry legal and regulatory consequences. Evidence obtained via scientific methods, such as biological, chemical, or analytical testing described in the general forensic science literature, is intended to help investigators determine whether a crime has taken place rather than to prove guilt on its own. Weaknesses in how material is collected, handled, or interpreted can be challenged, which is why the discipline emphasizes rigorous, repeatable methods.

It is important to note that the general definition of forensic evidence is set at a legal and scientific level. Its application to a specific domain such as payment card breach investigation depends on the applicable investigative standards, chain-of-custody controls, and jurisdictional rules. Those specifics are out of scope for this general term and should be confirmed against the relevant published requirements rather than assumed from the general definition.

Who it's relevant to

Breach Investigators and Incident Responders
Teams examining a suspected payment breach draw on the general investigative discipline of forensic evidence to establish what happened. They should apply the domain-specific investigative standards and chain-of-custody controls that govern payment card incidents rather than relying on the general legal definition alone.
Compliance and Legal Teams
Because forensic evidence may be presented in a court of law, compliance officers and legal counsel have an interest in how material is collected, handled, and documented. The applicable jurisdictional rules and published requirements determine what is admissible and should be confirmed for the specific matter.
Fraud Analysts and Merchant Risk Teams
Analysts investigating suspected fraud rely on scientifically obtained material to help determine whether an incident constitutes a crime. Understanding that forensic findings are intended to support, not replace, a broader investigation helps set realistic expectations for what such evidence can and cannot establish.
Acquirers and Payment Processors
Organizations that may commission or receive forensic findings after a suspected breach benefit from understanding the scientific basis and limitations of that evidence, and from confirming that the investigative standards and controls applied match the relevant published requirements for their region and card brand relationships.

Inside Forensic Evidence

System and Application Logs
Records from operating systems, applications, firewalls, IDS/IPS, and authentication systems that may capture the timing, source, and nature of unauthorized activity. Their evidentiary value depends on retention, integrity, and time synchronization.
Volatile Data
Transient information such as running processes, active network connections, memory contents, and cached data that may be lost when a system is powered off. Capturing it typically requires acting on a live system before shutdown.
Disk and Storage Images
Bit-for-bit copies of storage media taken to preserve the state of a system for analysis without altering the original. Working from images rather than live systems helps protect the integrity of the underlying evidence.
Chain of Custody Documentation
Records that track who collected, accessed, transferred, and stored each piece of evidence, and when. This documentation supports the reliability and admissibility of evidence in investigations or legal proceedings.
Indicators of Compromise
Artifacts such as malicious file hashes, suspicious IP addresses, unexpected registry or configuration changes, and anomalous account activity that may indicate a breach and can help scope the affected environment.
Cardholder Data Exposure Artifacts
Evidence relevant to whether cardholder data (such as PAN or expiration date) or sensitive authentication data (such as full track data, CAV2/CVC2/CVV2/CID, or PIN blocks) was present, accessible, or exfiltrated. Presence of stored sensitive authentication data after authorization is itself a significant finding, since it must not be retained even when encrypted.

Common questions

Answers to the questions practitioners most commonly ask about Forensic Evidence.

Does collecting forensic evidence mean the same thing as running a PCI DSS assessment?
No. A PCI DSS assessment evaluates whether controls meet the applicable requirements of the current standard, while forensic evidence collection is a distinct investigative activity, typically triggered by a suspected or confirmed compromise, aimed at preserving and analyzing artifacts to determine what happened. In many card brand contexts, a forensic investigation following a suspected breach is conducted by a PCI Forensic Investigator (PFI) under card brand rules rather than by the entity's normal assessor, and its objectives and outputs differ from an assessment. Confirm the specific expectations against the current published requirements and applicable card brand programs.
If sensitive authentication data appears in forensic evidence, does that just prove it was encrypted safely?
No. Sensitive authentication data, such as full track data, CAV2/CVC2/CVV2/CID, and PINs or PIN blocks, must not be stored after authorization, even when encrypted. If forensic evidence reveals such data present after authorization, that indicates a storage issue regardless of whether it was encrypted, because the prohibition applies to storage of the data itself, not only to storage in cleartext. This is different from certain cardholder data, which may be stored under defined controls. Encryption changes how data is protected but does not authorize retaining sensitive authentication data.
What sources of forensic evidence are typically relevant when investigating a payment environment compromise?
Relevant sources may include system and application logs, network traffic records, memory captures, disk images, file integrity monitoring output, authentication and access records, and change management artifacts, among others. The value of each source depends on what was retained, its integrity, and how it was collected. Because logging scope, retention, and configuration vary by environment and by the version of the standard applied, confirm which sources exist and are trustworthy in the specific environment rather than assuming any particular source is available.
How should forensic evidence be preserved to maintain its integrity?
Preserving forensic evidence generally involves establishing and documenting a chain of custody, capturing data using methods intended to avoid altering the original, verifying integrity through mechanisms such as cryptographic hashing, and restricting access to authorized personnel. The intent is to help maintain the reliability and admissibility of the evidence. Specific procedures should follow the organization's incident response plan and any applicable card brand or legal requirements, which can vary by region and by investigating party.
Who is typically responsible for collecting forensic evidence after a suspected breach?
Responsibility depends on the situation and the applicable card brand rules. For suspected or confirmed account data compromises subject to card brand programs, a PCI Forensic Investigator (PFI) may be engaged to conduct the investigation, while internal incident response teams may handle initial containment and preservation. Roles, triggers, and reporting obligations vary by card brand and region and can change over time, so confirm current program requirements and coordinate with acquirers and legal counsel before altering the environment.
How can premature remediation affect forensic evidence?
Actions taken to contain or remediate an incident, such as rebuilding systems, clearing logs, or restoring from backups, can overwrite or destroy artifacts needed for a forensic investigation. Because of this trade-off, incident response plans commonly emphasize preserving evidence before or in parallel with remediation, and coordinating with any assigned investigator and with the acquirer. The appropriate balance between rapid containment and evidence preservation depends on the specific incident and applicable requirements, so decisions should be documented and made with relevant stakeholders.

Common misconceptions

Forensic evidence collection is only necessary once a breach has been confirmed.
The ability to collect usable forensic evidence depends on controls put in place beforehand, such as adequate log retention, time synchronization, and file integrity monitoring. If those controls are absent before an incident, key evidence may no longer exist by the time an investigation begins.
Analysts should investigate directly on the affected production system to see what happened.
Working on a live original system can alter or destroy evidence, including volatile data and file metadata, and can compromise chain of custody. Investigators generally preserve volatile data first where appropriate, then work from forensic images rather than the original media.
A forensic investigation definitively proves exactly which records were stolen and guarantees the full scope of a breach.
Forensic findings help scope an incident but are constrained by available evidence. Gaps in logging, log tampering, or short retention windows can leave the full scope uncertain. Conclusions are typically expressed in terms of what the evidence supports rather than as absolute certainty.

Best practices

Establish and validate logging, log retention, and time synchronization before an incident so that usable evidence exists when needed; confirm requirements against the current published PCI DSS version rather than assuming fixed requirement numbers.
Preserve volatile data appropriately and capture forensic images before making changes to affected systems, so analysis is performed against copies rather than original media.
Maintain documented chain of custody for every piece of evidence, recording who collected, accessed, and transferred it and when, to support integrity and potential admissibility.
Engage qualified forensic responders and, where card brand or acquirer rules require it, a PCI Forensic Investigator, following the applicable network and regional obligations, which vary and change over time.
Scope the investigation to determine whether cardholder data or sensitive authentication data was present or exposed, treating any post-authorization storage of sensitive authentication data as a distinct and serious finding.
Express findings in qualified terms tied to the available evidence, noting logging gaps or retention limits that may leave the full scope uncertain, and avoid overstating certainty about what was accessed or exfiltrated.