Final answer:
A CPA should comply with the provisions of relevant professional standards and guidelines when determining whether a client's websites meet defined security and processing integrity criteria.
Step-by-step explanation:
When an entity engages a CPA to determine whether their websites meet defined criteria for security and processing integrity, the CPA should comply with the provisions of the relevant professional standards and guidelines. In this case, the CPA should adhere to the guidelines set forth by the American Institute of Certified Public Accountants (AICPA) and the International Standards on Assurance Engagements (ISAE). These standards provide a framework for the CPA to assess the security and processing integrity of the client's websites, ensuring compliance with industry best practices and regulatory requirements.