Confidential IRS data reveals that David Hoeft, chief investment officer of mutual fund giant Dodge & Cox, was one of many investment managers who bought and sold the same stocks their company was trading.

For decades, regulators have tried to clamp down on front-running, the term for when investment professionals make personal purchases or sales of securities when they know that their employers or clients are about to buy or sell the same securities. But a massive assemblage of confidential stock trading data obtained by ProPublica reveals that the practice may be continuing on a notable scale.