The cyber attack targeting Sony Pictures might have been just a rehearsal for a certain hacker group from North Korea, Reuters reports, as the country’s elite army of hackers might be working on more complex operations against more important targets in rival states. Though not confirmed to be responsible for the massive Sony hack, North Korea is currently the main suspect, according to recent reports.

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Rather than going after private companies, such as Sony, hackers backed by the North Korean government might have other targets in mind, including mobile operators and energy grids in rival countries such as the U.S. and South Korea.

According to defectors familiar with North Korea’s hacking efforts, the totalitarian state has been working for years on perfecting cyber attacks that could take out computer systems that control public services like carriers and utilities.

“North Korea’s ultimate goal in cyber strategy is to be able to attack national infrastructure of South Korea and the United States,” Kim Heung-kwang a North Korean former computer science professor who escaped to the South, said.

“The hacking of Sony Pictures is similar to previous attacks that were blamed on North Korea and is a result of training and efforts made with the goal of destroying infrastructure,” he added.

“They have trained themselves by launching attacks related to electronic networks,” Jang Se-yul, also a defector familiar with the North’s cyber warfare unit, said.

“The ultimate target that they have been aiming at for long is infrastructure,” Jang said.

The North Korean army apparently has a sophisticated cyber-warfare cell at its disposal, called Bureau 121, which is “staffed by some of the most talented computer experts in the country.”

North Korea is believed to have attacked the South in various hacking operations so far, targeting banks, broadcasters and energy utilities.

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