For the last two decades, officers and directors at US public companies seeking to trade illicitly on inside information had an almost infallible get-out-of-jail-free card.

All they had to do was use pre-arranged trading plans when they bought and sold their companies’ shares. The odds the government would target them for enforcement actions were slim. It was an unintended consequence of a 2002 regulation called Rule 10b5-1 that academic research shows was abused by some executives.