South Korea has warned it would immediately retaliate against the North and has held unscheduled military exercises after series of threats from Pyongyang. A week ago the North threatened to launch rocket attacks on media offices in the South.
Seoul’s armed forces held the exercise on Monday because of a "series of peculiar activities", a Defense ministry spokesman told AFP.
It was ordered by the country’s Defense Minister Kim Kwan-Jin so the military could "immediately retaliate against sources of provocations and supporting forces as well as core command forces".
The drill involved the ballistic missile command, front-line artillery units and the Air Force, South Korean media has reported.
Tension increased between the neighboring states after the North’s threat against South Korean media outlets for what Pyongyang has called critical coverage of its internal policies.
The two countries often exchange threat of military action, but have managed to avoid a full-scale armed conflict.
As the North has accused the South’s media of propaganda, one of the newspapers on the Pyongyang’s “to do” list – JoongAng Ilbo newspaper – survived a severe cyber attack on Saturday.
Its sister paper Korea JoongAng Daily was also a victim of an attack, which temporarily paralyzed database servers and websites.
The connection to the site www.joongang.co.kr was cut off. A photo of a white cat and the statement "Hacked by IsOne" was posted instead.
It also said a message suggested that more media sites would be hacked on two days, the 19th and the 29th of June.
South Korean police are investigating the North’s possible involvement in the hacking although North Korea only threatened a missile strike, not a cyber attack.
"We have never seen a strong attack like this before," the paper quoted Jong Seok-Hwa, chief investigator of the national police force's Cyber Terror Response Center, as saying.
Seoul believes Pyongyang has an elite team of hackers and has earlier blamed the North for other attacks of this type including the one against government and financial institutions’ websites in July 2009 and March 2011.
In May the South accused Pyongyang of jamming the GPS systems of hundreds of civilian aircraft and ships in South Korea between April 28 and May 13.
The North has always rejected the South's accusations as "sheer fabrication".