We do a sample of employees quarterly and we have about 160 employees. The audit department does the review and we are looking for unusual activity, following bank policies (code of ethics) and account setup for appropriate coding. I don't think it is a requirement. Although it won't catch all fraud, it may catch some.
If I remember correctly, there were a lot of variations in past discussions. It would depend on your bank size and what options you have available to you.
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Do what you can, with what you have, where you are.
~Theodore Roosevelt~