"We do not rule out the possibility of North Korea being involved, but it's premature to say so, " Defence Ministry spokesman Kim Min-seok said.

BBC: South Korea network attack 'a computer virus'

South Korean Defense Ministry spokesman Kim Min-seok told reporters Tuesday there were no signs that North Korea could conduct additional nuclear and missile tests anytime soon, or launch some other provocation.

NPR: US Institute: All Quiet At NKorea Test Sites

On Thursday, a spokesman for the South Korean Defence Ministry, Kim Min-seok, said Pyongyang had been observed carrying out "various drills involving the army, navy and air force, " and that further exercises were being prepared, the Yonhap news agency reports.

BBC: North Korea ramps up nuclear rhetoric as UN vote looms