"The companies are located throughout the country, and include Fortune 500 companies as well as smaller [companies]," Cox told the Senate Banking Committee on Wednesday. "They span multiple industry sectors."

Cox told reporters in San Francisco on July 20 when he announce the indictment of former Brocade Communications Systems Inc. executives in connection with the probe that the SEC was investigating more than 80 companies.

Cox told lawmakers they should not expect each probe to result in indictments. "At the same time, we have to expect other enforcement actions will be forthcoming in the future," he said.

Dozens of companies have been implicated in the scandal. Most of the allegations have centered on the practice of backdating stock options—retroactively granting options on dates when a company's stock price is relatively low, maximizing the potential profits for the option holder.

The U.S. Justice Department has filed multiple charges against two of the former Brocade executives implicated by the SEC, as well as three former employees of software vendor Comverse Technology Inc. The SEC also filed charges against the former Comverse executives.

In Northern California, U.S. Attorney Kevin Ryan has created a stock options backdating task force to investigate allegations that Silicon Valley companies retroactively changed grant dates for stock options. Ryan has refused to say how many companies he is investigating, but a number of companies have disclosed in SEC filings that they have received subpoenas from his office.

Cox outlined a number of policy and legislative changes that have been implemented in recent years to prevent stock options backdating, including the Sarbanes-Oxley financial disclosure law. Most stock options backdating is alleged to have occurred prior to the enactment of Sarbanes-Oxley, which requires that stock options grants for top executives be reported to the SEC within two days.

A new accounting rule, Cox said, has eliminated the incentive to grant "at-the-money" options—options that are immediately profitable because they are granted below the stock's current price. New SEC executive compensation rules now require "a complete quantitative and narrative disclosure of a company's executive compensation plans and goals," Cox said. The rules will soon be complemented by more accounting guidance, Cox told lawmakers.

"Each of these steps by itself is an important contribution to preventing backdating abuse," Cox said. "In combination, they have effectively slammed the door shut on the easy opportunities to get away with secretive options grants."