Stock options are rights to buy shares at set prices in the future, and were widely used by technology companies and others starting in the late 1990s to lure employees with the promise of future riches rather than high salaries.

Academic studies have shown many companies tended to award options on dates when company share prices hit historic lows, raising suspicions that companies were "backdating" options to maximize their financial benefit to employees.

By October, at least 140 companies disclosed investigations into stock backdating and more than 20 executives lost their jobs.

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(University of Iowa finance professor Erik Lie, whose work on backdating is widely credited with exposing the scandal latest scandal to rattle corporate America.)