Federal prosecutors have unsealed criminal conspiracy charges against three former senior executives at a New York software maker, accusing the men of turning back the clock to reward themselves and favoured employees with millions of dollars in stock profits.

Authorities accused the former Comverse Technology officials of misleading investors by backdating stock option awards and creating a slush fund to benefit top employees without properly disclosing the compensation to board members.

The rapidly evolving scandal over stock options comes as shareholders and securities regulators are expressing renewed concern about excessive executive compensation and whether companies are fudging the amount of pay and perks they offer senior management.

The criminal charges ratchet up pressure on the scores of US businesses - from Apple Computer to Monster Worldwide - that have launched internal probes of past stock option practices in recent weeks.

Well over a dozen companies have delayed filing financial reports as they await the results of investigations. The FBI is pursuing 45 backdating cases, and regulators at the Securities and Exchange Commission are examining 80 companies, law enforcement officials said.

Acting assistant FBI director James "Chip" Burrus called the behaviour a "deceitful abuse of corporate power" and said that options backdating represents "the newest trend in investor fleecing" after financial scandals at Enron and WorldCom in recent years. "It's the corporate equivalent of placing a bet after the race has been won," Mr Burrus told reporters.

Options give employees the right to buy stock at a set price and a specific time. People profit based on the difference in price on the date of the award and the date they actually sell the stock. In backdating cases, executives selected award dates after the fact that happened to mark low points in the company's stock price, increasing the likelihood that they would receive a windfall. Although backdating options is not necessarily illegal, companies must follow certain steps.

In this week's charges, the government cited options awards made to "phantom" employees, alleged tampering with a computer database, and potentially damaging statements that the accused Comverse executives made to company lawyers, including a comment that "everyone" across the technology sector had engaged in the practice.