New clues emerge after four-year hacking spree in South Korea

Researchers with US security software maker Symantec Corp say they have uncovered digital evidence that links cyber attacks on South Korea dating back four years to a single hacking group dubbed the "Dark Seoul Gang."

Eric Chien, technical director with Symantec Security Response, said late on Wednesday that his firm made the connection while reviewing malicious software code used to launch attacks that disrupted some South Korean government websites earlier in the week.

He said that the evidence did not uncover the identity of the gang members.

North Korea has been blamed for previous cyber attacks on South Korean banks and government networks, although Pyongyang denies responsibility and has said it has also been a victim.

Symantec researchers found chunks of code that were identical to code in malicious programs used in four previous significant attacks, the first of which happened on July 4, 2009, according to Chien.

"We know that they are one gang," he said. "It is extremely well coordinated."

He estimates that the group has between 10 and 50 members, based on the sophistication of the code and the complexity of their attacks.

The July 4, 2009, attack wiped data on PCs and also launched distributed denial of service attacks that disrupted websites in South Korea as well as the United States.

In March of this year, the gang knocked tens of thousands of PCs off line at South Korean companies by destroying data on their hard drives, Chien said. It was one of the most destructive cyber attacks on private computer networks to date.

Symantec published its report on the gang on its website.

A hacking attack on Tuesday, the anniversary of the start of the Korean War in 1950, brought down the main websites of South Korea's presidential office and some local newspapers, prompting cybersecurity officials to raise the alert. 

(Reporting by Jim Finkle; Editing by Eric Beech)