South Korea is fingering its northern neighbours for an attack last month against a navy defence contractor.
North Korea's regime says the attribution is political and dubbed the attacks fabricated.
Details of the hack of Hanjin Heavy Industries have not been disclosed but local broadcaster Yonhap reports the government has kept open the possibility of North Korean involvement.
"After identifying signs that Hanjin Heavy Industries may have been hacked on April 20, the Defense Security Command is currently leading a security investigation into whether any military secrets were leaked and whether North Korea was involved," unnamed officials told Yonhap.
The contractor is responsible for the production of Seoul's latest naval vessels and amphibious assault vehicles including the ROKS Dokdo.
It is the latest security breach of South Korea's defence industry since hackers in November popped contractor LIG Nex1 and the Agency for Defense Development, both responsible for building its AESA radar.
North Korea is said to have well-structured elite hacking teams. One unit dubbed Bureau 121 is claimed to be situated in the nation's spy agency the General Bureau of Reconnaissance, and is fingered for intrusions into network infrastructure of foreign states.
Security researchers identified the so-called Lazarus Group as the unit behind the 2014 flaying of Sony Pictures, a hack which the US pinned firmly on Pyongyang. ®