The three credit card firms hit by recent massive data leaks may have to pay up to 170 billion won ($158 million) in compensation to their clients to settle class action lawsuits, data showed on Monday.

Last month, the Financial Supervisory Service, the country's financial watchdog, revealed that some 20 million clients' personal data, including bank account numbers, addresses and credit ratings, have been leaked from the three card issuers -- KB Kookmin Card Co., NH Nonghyup Card Co. and Lotte Card Co.

The largest-ever data breach has already prodded angry clients to sign up to file a class action lawsuit against the card firms for the data theft.

In a regulatory filing, KB Kookmin Card said that it may fork over up to 86 billion won in compensation to its clients, citing a similar court case.

In February last year, SK Communications Co., the operator of local search engine Nate, was ordered by a court to pay 200,000 won each in compensation to 2,882 users for failing to protect customer data.

KB Kookmin Card estimated that about 1 percent of its clients whose data were stolen may participate in the class action suit and that it would pay the same amount of compensation as SK Communications.

Based on KB Kookmin Card's calculation, Lotte and Nonghyup may each pay 35 billion won and 50 billion won to their clients who join the suit.

The credit card firms are already suffering losses as millions of their clients have canceled their plastic cards or asked for new ones, which will cost them up to 40 billion won.

The country's financial regulator is also set to impose a three-month suspension on them as punishment for the data theft, banning them from signing on new customers.

Industry sources said some insurers such as Prudential Life Insurance Co. were also found to have been lax in data security.

The insurer allegedly allowed external auditors access to their clients' information without their consent in January 2012. Three senior officials were reprimanded and the firm was fined 6 million won, the sources said. (Yonhap News)