The U.S. regulator overseeing auditors was rocked by criminal charges as federal prosecutors accused three former employees of leaking inside information to KPMG so it could improve its audit results.

The allegations are a major embarrassment for the Public Company Accounting Oversight Board, a regulator that was meant to restore public confidence in the audit industry after accounting scandals at Enron and WorldCom cost investors billions of dollars. Claims that employees shared confidential information with a top audit firm raise doubt about whether the PCAOB is up to the job.

They're also another black eye for KPMG, one of the Big Four accounting firms. The company paid $456 million in 2006 to avoid criminal charges that it helped wealthy clients dodge $2.5 billion in taxes. The firm is accused of poaching PCAOB officials and using their contacts to get warnings about pending inspections.