Hotlines are typically classified based on their operational and administrative models. Common classifications include who operates the service (e.g., in-house vs. third-party) and its availability (e.g., full-time/24-7 vs. part-time/business hours). While a hotline is a type of detective control because its purpose is to detect fraud and misconduct, "detective hotline" is not a standard classification for the hotline system itself. The term describes the control's function within the internal control framework, not a specific type of hotline implementation.

A. Part-time hotline: This is a valid operational model where a hotline is only available during specific hours, such as standard business hours.

B. Full-time hotline: This is a common model, often considered a best practice, where a hotline is available 24 hours a day, 7 days a week.

C. Third-party hotline: This is a widely used administrative model where an external vendor is contracted to manage the hotline, which can enhance anonymity and credibility.

1. Association of Certified Fraud Examiners. (2023). Fraud Examiners Manual, International Edition. Section 4.405, "Reporting Programs and Whistleblower Protections." The manual discusses various aspects of implementing reporting mechanisms, including the use of third-party providers and ensuring constant accessibility (implying full-time vs. part-time models), but does not classify a hotline type as "detective."

2. KPMG. (2015). The whistleblower hotline: A survey of hotline practices at U.S. public companies. This report details common hotline practices, including outsourcing to third-party providers (p. 6) and hours of operation (p. 7), which directly correspond to the valid options. The term "detective hotline" is not used as a classification.

3. Brink, A. G., & Ernest, E. (2018). Designing World-Class Business Ethics and Compliance Programs: A Study of the Top 10 Most Ethical Companies. Journal of Management Accounting Research, 30(3), 51–73. https://doi.org/10.2308/jmar-52039. The study identifies best practices for reporting mechanisms, including "24/7 availability of a hotline" (full-time) and the use of "third-party vendors" (p. 61), confirming these as established types or models.