South Korea's telecom ministry said Friday it will launch an investigation into the latest hacking incident at KT Corp. that led to millions of customers' personal data being leaked.

The Incheon Metropolitan Police Agency said on Thursday it arrested three suspects for allegedly hacking into the company's website and stealing data of some 12 million clients of the mobile carrier.

The Ministry of Science, ICT and Future Planning said it will establish a team of government officials and online security specialists to find out the details of the incident with the cooperation of the Korea Communications Commission.

According to the police, the leaked data include the clients' names, resident registration numbers and bank account information. The hacking attacks took place over the course of one year starting last February, gathering up to some 300,000 pieces of information in a given day, they said.

The ministry ordered KT to provide the victims with details and backgrounds of the incident and establish a system on its website to allow users to check if their information was included in the hacked data.

"Under cooperation with related bodies, we will make our best effort to make sure customers' data are not circulated," KT chief Hwang Chang-gyu said in a meeting with reporters Friday.

"We will start from the beginning by reprimanding those who are responsible," Hwang added. "KT will focus on improving security systems as soon as possible."

The ministry said it will operate an around-the-clock service center to receive reports on damages incurred from the leak and warned users to be aware of calls and texts by people impersonating KT staff.

It added its investigation showed the systems of SK Telecom Co. and LG Uplus Corp., the country's other two major mobile carriers, were not found to have similar weaknesses to KT.

In 2012, personal information of about 8.7 million mobile phone subscribers was stolen from KT by hackers, who sold the information to telemarketers, who then contacted customers whose contracts were nearing expiration or considered likely to change subscription plans.

The police said it plans to summon security specialists from KT next week for further investigation into the incident. (Yonhap)