Former Comverse Technology Inc. executive William F. Sorin pleaded guilty to a conspiracy charge Thursday in a stock-options backdating scheme.

Mr. Sorin, the New York voice mail-software maker’s ex-senior general counsel, pleaded guilty to conspiracy to commit securities fraud, mail fraud and wire fraud at a hearing before U.S. District Judge Nicholas G. Garaufis in federal court in Brooklyn on Thursday.

“On this issue, I failed as a lawyer and did a disservice to our shareholders,” said Mr. Sorin, 57 years old.

Mr. Sorin, the second former Comverse Technology executive to plead guilty in the matter, faces up to five years in prison on the charges.

Prosecutors also are seeking $51 million in restitution.

David Kreinberg, the company’s former chief financial officer, pleaded guilty to securities fraud and conspiracy to commit securities fraud, mail fraud and wire fraud at a hearing last week.

Their pleas come as federal regulators take a harder look at the backdating of option grants. The grant practices at more than 100 companies are being probed and a number of executives have lost their jobs.

Mr. Sorin, Mr. Kreinberg and ex-Comverse Chief Executive Jacob “Kobi” Alexander were all charged in August with conspiracy to commit mail fraud, securities fraud and wire fraud in an alleged scheme to improperly backdate options at the company. The SEC also has separately filed civil charges against the men.

Mr. Alexander, an Israeli citizen and permanent resident in America, fled the country and was arrested in the African nation of Namibia last month. The American government is seeking his extradition from Namibia.

He has since been indicted on charges of conspiracy, securities fraud, making false filings with the SEC, mail fraud, wire fraud, money laundering and engaging in unlawful monetary transactions.

Prosecutors have alleged that Mr. Alexander and others engaged in a scheme to backdate millions of stock options for themselves and other employees when Comverse’s stock was trading at periodic lows. The improper grants occurred between 1998 and 2002, according to court documents.

The government also has alleged that Mr. Alexander and others used fictitious names to generate hundreds of thousands of backdated options, which were parked in a “secret slush fund” designed to evade the requirements of Comverse’s stock-option plans. Mr. Alexander then unilaterally awarded options from the slush fund to favored employees, according to prosecutors.

The slush fund was first named I.M. Fanton, after “Phantom of the Opera” and later changed to “Fargo” — based on the Coen brothers’ movie of the same name, according to court documents.