A prosecutor in South Korea has claimed that a cyber attack conducted by North Korea is behind an ongoing outage at one of the country’s major banks.  

Two weeks ago, a system crash at South Korea’s NH Bank shut down banking transactions, meaning that many customers could not withdraw cash or make payments. The outages lasted for more than a week.

Now, according to the Reuters news agency, a senior prosecutor from the Seoul Central Prosecutors’ Office has said the outage was the results of "unprecedented act of cyber terror" originating in North Korea.

According to local news sources, the breach affected systems operated by NH Bank’s IT services supplier IBM. "The laptop of the IBM worker at issue ordered the deletion of execution files of our key systems, which involved more than one hundred IBM servers," a spokesperson for the bank told the Korea Times last week. "This generated the service failure."

"However, the employee seems to flatly deny any wrongdoing," the spokesperson added. "We need to wait until ongoing investigations are completed to know exactly what or who caused all the trouble.’’

At the time, the paper cited experts saying that the fact the IBM’s disaster recovery system failed to kick in suggested that it was more just an accidental outage.

South Korea has blamed the North, with which it has been at war for decades, for cyber attacks in the past. Just last month, the South’s National Police Agency said 30 government websites had been taken down by a denial of service attack originating in North Korea.

However, some observers have questioned the likelihood a sophisticated cyber attack originating in the country, given its dated IT infrastructure.

In 2009, South Korea’s National Intelligence Service said that a string of attacks on banks, businesses and government agencies that took place on the 4th of July, America’s Independence Day, had been the work of North Korea or “a pro-North Korean force”.

But security researcher Joe Stewart remarked at the time that there was nothing about those attacks to suggest they were state sponsored.