Which entity is responsible for defining rules for forensic investigations related to data compromises?

The payment brands are indeed responsible for defining the rules for forensic investigations related to data compromises. They create the guidelines and standards that govern how such investigations should be conducted when a data breach occurs involving payment card information. This includes setting forth requirements for forensic analysis, qualifications of forensic investigators, and protocols for preserving evidence, all aiming to ensure a consistent and effective approach to investigating and mitigating data security incidents within their ecosystems.

Merchant acquirers play a role in facilitating transactions and ensuring compliance among merchants but do not set the rules for forensic investigations. Quality Security Assessors focus on evaluating compliance with standards such as PCI DSS, and while they might assist in investigations, they do not define the rules for how these investigations are conducted. External auditors may review and assess compliance and practices but similarly do not define the protocols for forensic investigations; these fall under the purview of the payment brands.