Story highlights South Korean investigators say they have proof that North Korea is launching cyberattacks

Reports say the North is investing heavily in digital warfare

December attack on banks in South Korea caused about $820 million worth of damage, a report says

Seoul, South Korea (CNN) On March 20, 2013, a cyberattack brought chaos to several banks and media outlets in South Korea.

Then more ominously on December 23 last year, computers at the country's nuclear operator were breached. Again cybercrime was suspected.

The source of these attacks? North Korea. And South Korean investigators say they have proof -- the actual malicious codes used in the attacks. They shared this data with CNN.

The 2013 attack, known as "Dark Seoul," paralyzed an estimated 48,000 computers at a number of major banks and broadcasters, disrupting network systems and wiping their hard disks clean.

"It would try to delete essentially all your files... then restart the system. You would come back up and nothing would be there," Joshua James, a digital forensic expert, told CNN.

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