Any member of the American Institute of Certified Public Accountants who performs an audit must be peer reviewed. Cutting through the technical jargon, this means another CPA comes in and looks at your work product and passes judgement about whether you are doing your job properly.
Brokerage companies usually must be audited by firms that are registered under the Public Company Accounting Oversight Board (PCAOB) which was created under the Sarbanes-Oxley Act to help prevent fraud (how’s all that working out?). The SEC exempted companies like Madoff Securities from this audit requirement, which means that the firm auditing Bernie Madoff did not have to be registered with PCAOB or be peer reviewed. What we have here is a phenomenal failure of regulatory oversight.
Remember that Bernie Madoff was chairman of the NASDAQ Stock Market for a period of time.
Source: AICPA Issues Briefing