Undisclosed payments made by vendors to employees of purchasing companies are referred to as:

Detailed Explanation:

Rationale for Correct Answer: Kickbacks are undisclosed payments made by vendors to employees of purchasing companies to secure favorable treatment. They are a classic form of bribery under the corruption classification of the Fraud Tree.

Analysis of Incorrect Options:

A. Bid-rigging – Involves collusion among bidders, not secret payments.

C. Presolicitation – A phase in procurement fraud, not the scheme itself.

D. None of the above – Incorrect, as kickbacks are the precise answer.

Key Concept: Kickbacks — secret vendor payments for favorable purchasing treatment.