South Korean police have arrested two computer programmers on suspicion of hacking personal data of 8.7 million KT subscribers.
KT Corp, South Korea's No. 2 wireless service provider, has apologised after million of mobile phobe subscribers had their personal data hacked.
It is the latest in a string of large-scale personal information hacking cases in one of the world's most wired countries.
KT claims a mobile service subscription membership of 16 million.
Police were also investigating seven others suspected of having purchased and used the hacked KT data, which included names, resident registration numbers and phone numbers.
"We deeply apologise for worrying you," KT said in a statement, adding that it had blocked any further illegal access to data.
The hacking began in February.
In November, more than 13 million subscribers of Nexon Korea Corp, a leading game developer, fell victim to a hacking attack.
Months before the Nexon Korea case, information of up to 35 million users of an internet portal and blogging site operated by SK Comms, the country's top mobile service provider, was attacked by hackers from China