"The group also hacked into the computers or phones of lawmakers' staff, journalists, North Korean defectors, and lawyers," he added.

Moon Jong-hyun of cybersecurity firm ESTsecurity in Seoul told the Chosun Ilbo on Sunday, "A North Korean hacker group launched a spear-phishing attack on specific individuals or companies rather than many unspecified people or corporations by planting malware in their computers or smartphones."

North Korean hackers stole private data including phone numbers and text messages, from the phone of Thae Yong-ho, the former No. 2 in the North Korean Embassy in London who is running for a National Assembly seat here.

The group is identified as "Kimsuky" which hacked Korea Hydro and Nuclear Power in 2014.

This suggests that the safety of Thae, who uses the name Thae Gu-min to evade tracking since his defection in 2016, from his murderous former employers might be compromised.

According to ESTsecurity, the group's cyberattack on Thae's phone was discovered in the process of tracking down an earlier cyberattack on the phone of a South Korean journalist handling political affairs last year.

They tried to hack the journalist's phone under the pretext of providing "information on North Korea" by attaching a malicious website link through KakaoTalk.

But the reporter became suspicious and asked ESTsecurity to track it down. ESTsecurity retraced the messages and was able to gain access to the hackers' server, where it found a variety of data stored.

"The hackers were using a Samsung Galaxy," Moon said. "We found that the server had a lot of data stolen from Thae's phone." Thae was told of the hack and the problem was solved, the company said.

"Normally, hackers approach specific individuals through social media or messaging apps to make them set up a malware and infect their smartphones or computers," Moon added. "If you use infected computers or smartphones, all data will be transmitted to hackers.