According to sources requesting anonymity, US regulators are investigating Ruth Madoff, the 67-year-old wife of alleged fraud mastermind Bernard Madoff, after the Securities and Exchange Commission (SEC) found evidence she may have helped track payments in a $50 billion Ponzi scheme.

Two people with knowledge of the probe on December 14 said that though the authorities have not accused Ruth of wrongdoing, they are examining why her name appears on related transactions.

Ira "Ike" Sorkin, a New York attorney at Dickstein Shapiro LLP, which represents the Madoff couple, said: "Ruth is not charged with anything. The SEC has not sought to freeze her assets. She's under no bail conditions."

Bernard Madoff, 70, who was arrested December 11, was charged with a single count of securities fraud. In court documents, prosecutors and the SEC said he had said his investment advisory business was "all just one big lie." His wife and his brother, Peter, were the only people willing to sign a $10 million bond to secure his release.

Judge Gabriel Gorenstein, who is overseeing criminal proceedings against Madoff, ordered the couple to surrender their passports. The couple appeared in court on Wednesday to sign documents to give up homes in Montauk, New York, and Palm Beach, Florida, if Bernard Madoff flees.

In fact, Madoff will be subject to home detention and electronic monitoring with a 7 p. m.-to-9 a. m. curfew. Court documents showed that Madoff's home detention was required because he failed to secure the required number of co-signers for his bail bond.