South Korean soldiers stand guard at the border village of Panmunjom between South and North Korea at the Demilitarized Zone (DMZ) on February 27, 2013 in South Korea. - 

South Korea is still recovering from an apparent cyberattack earlier this week that shut down cash machines, froze debit card transactions, and caused computers to go dark at banks and several media outlets. South Korean officials suspect North Korea, but proving that may be difficult. Last week, North Korea had accused the South of getting into its computers.

"All you need is a computer and grudge really to cause tremendous harm to a country's critical infrastructure," says Michael Dubose, head of cyber-investigations at the corporate risk consulting firm Kroll.

North Korea may not be the most technologically sophisticated country, but that's not required for a hack like this, Dubose says.

"On the underground Internet, you can purchase almost any type of software exploit that you can imagine. You can even purchase hackers for the right price," says Dubose.

Follow David Brancaccio at @DavidBrancaccio