By VOA News

U.S. investigators say they have cracked one of the biggest Wall Street insider trading rings since the 1980s.

Prosecutors have arrested 13 people who are believed to have made as much as $15 million from insider trading schemes. Some of those arrested are from Wall Street's top banks.

Employees from Bank of America, Morgan Stanley and UBS were accused Thursday of engaging in improper trading, conspiracy, fraud and bribery. Authorities say UBS Securities executive Mitchel Guttenberg is among those who face charges. They say he sold information to traders about the company's stock upgrades and downgrades by UBS analysts.

Authorities say the investigation has gone on for more than a year. The Securities and Exchange Commission has filed civil charges against 11 people and three entities allegedly involved in the case.