South Korea's telecom watchdog said Thursday it will impose a fine of 85 million won ($83,554) on the country's top fixed-line operator, KT Corp., over its recent data leak incident, a decision that will strengthen an ongoing class action lawsuit by the victims of the leak.

The Korea Communications Commission decided on the disciplinary measure after hackers stole some 11.7 million pieces of personal information from 9.81 million KT subscribers through the company's website between August 2013 and February this year.

"KT has failed to abide by the country's communication network law and did not detect and cut off abnormal access to its website, which led to the spill of personal information," the KCC said.

The commission said the methods used by the hackers were widely known, and given that KT had suffered a similar breach in 2012, the incident should have been preventable if the mobile carrier had carried out proper procedures.

"We hope that the decision will sound alarm bells for the businesses that handle personal data on a massive scale," said Choi Sung-joon, head of the KCC.

"We will also continue our efforts to examine the management of personal data by local firms, ease public concerns and limit damages to the people," Choi added.

The KCC has been investigating KT's leak since March to find out whether the company took appropriate actions to protect personal information. By local law, KCC can slap a fine of up to 100 million won on businesses for data leaks resulting from lax measures.

KT immediately protested KCC's decision, calling it "very confusing and regretful."

Appealing to KCC at its meeting Thursday, a KT official said the company has taken more precautionary measures than required by law and argued that its website became vulnerable because of the hackers' complex access methods.

"Regardless of the KCC's decision, KT again wishes to apologize for the leakage of personal data. We will prepare measures to establish an advanced security system to tackle complicated hacking technologies," KT said.

Industry watchers expect the KCC's penalty will help the victims of the leak in their lawsuits seeking monetary compensation.

Earlier in the day, the Citizens' Coalition for Economic Justice filed a 27.9 billion won lawsuit against KT, demanding 1 million won for each of the 2,796 victims of the incident. In March, another group of some 100 victims also filed a petition demanding 200,000 won each over the data leak. (Yonhap)