Names, social security numbers and credit card details from 20 million South Koreans have been stolen and sold to marketing firms, authorities say. An IT contractor working for a company that produces credit card scores was arrested for allegedly stealing the data from the firm, the Korea Credit Bureau, the BBC reported Monday. The contractor stole the data from databases run by three large South Korean credit card providers accessible through Korea Credit Bureau by copying it to a USB stick, authorities said. Managers at three marketing firms that allegedly purchased the data were also arrested, they said. The heads of the three credit card firms involved made a public apology for the data breach. South Korea's national financial regulator, the Financial Services Commission, said any financial loss by consumers would be the responsibility of the credit card companies. "The credit card firms will cover any financial losses caused to their customers due to the latest accident," the commission said in a statement. The data was easy to steal and sell because it was unencrypted, an FSC official said.