The government has verified that three rounds of investigation were conducted on 33-thousand servers feared to have been subject to a data breach during a hacking incident at the nation's largest mobile carrier SK Telecom(SKT).

At a parliamentary hearing on Thursday, Second Vice Science and ICT Minister Kang Do-hyun said a fourth investigation on the around 33-thousand servers is currently taking place.

The vice minister said there are believed to be more than 400-thousand when combining base stations and hardware servers, and it would be difficult to uniformly round up the rate of progress.

On April 18, SKT detected signs of a massive leak of users' SIM data due to a hacking attack, and have since offered to replace SIM cards for all of its users.