North Korean computer hackers were responsible for bringing down the network of a South Korean bank last month, prosecutors in Seoul said on Tuesday, in the latest of a string of cyber attacks thought to have originated from the secretive state.

Kim Young-dae, a senior prosecutor from the Seoul Central Prosecutors' Office, said an unprecedented act of cyber terror by a North Korean group caused the network breakdown of South Korea's agricultural banking cooperative Nonghyup.

The crash of Nonghyup's computer system affected millions of customers who were unable to use the bank's credit cards and ATMs for more than a week.

Prosecutors said the April 12 attack was meticulously prepared and executed by the same group that carried out cyber attacks on key South Korean government and business websites in 2009 and March this year. One of the internet protocol addresses used to break into the Nonghyup network was the same as one used two months ago for the distributed denial-of-service (DDoS) attack that originated from North Korea, the prosecution said. It said in a statement that the attack was a new type of cyber terrorism that targeted a private firm in an effort to destroy the financial system which is the backbone of (the South's) capitalist society.

North Korea was also blamed for disrupting GPS signals in the South in March, possibly in an attempt to disrupt joint military drills by South Korean and U.S. forces.

A South Korean defense white paper released earlier this year said cyber threats were becoming increasingly intelligent and virulent.

The two Koreas are still technically at war, having only signed a truce to end the 1950-53 Korean War, and tensions spiked sharply last year following two deadly attacks on the peninsula in which 50 South Koreans were killed.

(Reporting by Jeremy Laurence, editing by Jonathan Thatcher)

Cybercrime South Korea