Korea's second-biggest mobile operator hacked

South Korean police have arrested two hackers who stole personal data of 8.7 million customers of the nation's second-biggest mobile operator, the company said Sunday.

KT said the hackers -- formally arrested on Sunday -- had stolen data such as customers' names, phone numbers and residential registration numbers for five months since February and sold the information to telemarketing firms.

"The number of affected people account for nearly a half of about 17 million customers of ours," a KT spokesman told AFP, adding the company had alerted police on July 13 after detecting traces of hacking attacks.

Yonhap news agency, citing police, said the duo -- including a former veteran programmer at a local IT company -- had earned at least 1 billion won (about $880,000) by selling the stolen data.

Seven other people were also booked for buying the leaked data for telemarketing purposes, Yonhap said.

"We deeply bow our head in apology for having your precious personal information leaked... we'll try our best to make such things never happen again," KT said in a statement to customers.

Hacking attacks on major companies aimed to gain access to the personal data of their customers is a frequent occurence in South Korea, one of the world's most-wired nations.

Seoul authorities said in July last year hackers using an Internet address registered in China had gained access to South Korean major websites including web portal Nate.com and may have stolen the private data of 35 million users.

In November 2011, Seoul's top games developer Nexon saw personal information of 13 million users of its popular online game MapleStory stolen by hackers.

In March 2010, authorities launched a probe into the security systems of major retailer Shinsegae and 24 other companies after private data on 20 million customers was leaked.